Export for Screens: a ZIP export deflates its files

With `zip: true`, document.exportForScreens deflated nothing: every file
went into the archive stored. Each file is now deflated, or stored when
deflating does not make it smaller, as file.package's archive does. The
file list, the names and the reply's fields stay the same; `bytes` and
the archive's contents change. Entries keep the fixed 1980-01-01 date, so
the same files still give the same archive.

The deflating writer moves from package.rs into fileio/zip.rs as
`zip::deflate`, beside `zip::store`, and file.package calls it there with
its own date and error text. The test reader `zip::entries` reads
deflated entries too. The `zip` option's text in docs/mcp.md,
docs/control-protocol.md and the command's params says the files are
deflated.

docs/control-protocol.md

@@ -121,7 +121,7 @@ the two can still win that race.
 | `engine.execute` `document.exportForOffice` | `{}` / `{path?, ppi?: 72 \| 150 \| 300, transparent?, artboard?}` | File → Save for Office Documents…: without params opens `saveForOffice` (fields `ppi`, `transparent`, `artboard`; OK picks the file); with params writes the artboard as a PNG (`path`, else a picked file) → `{path}`, and the status bar shows the first of the export's `warnings` as Save As shows a save's notes. Headless it returns `{dataBase64, width, height, warnings}` |
 | Native file dialogs | any command with no `path` that needs one (`file.open`, `file.saveAs`, `file.place`, exports…) | on macOS (a sheet on the window) and Linux the dialog doesn't hold the window: the call returns `"cancelled"` at once, `ui.inspect` reports `fileDialog`, and when the person at the computer picks a file the command runs again on the document it was asked for. While it is open another dialog is refused: that call returns `"cancelled"` too, and the status bar (`ui.inspect` → `ui.status`) says `"A file dialog is open: choose there first"`; on macOS `app.quit`, `file.close` and `file.closeAll` return that message and the menu bar does nothing (#592, #867). On Windows the dialog is shown in line: the call returns once it closes. Pass `path` to skip the dialog |
 | Background Save / Export | `app.save`, `app.export {path}`, `file.save`, `file.saveAs`, `file.saveCopy`, `file.exportForScreens {folder, …}` | with the `backgroundSave` / `backgroundExport` preferences on (the default) the desktop app writes the file from a snapshot on a worker thread: the call returns `{path, background: true, status}` at once (`file.exportForScreens`: `{background: true, status}`, and the files are written into the folder from a snapshot taken at the call), `ui.inspect` lists the jobs still running in `background` (labels such as `"Saving a.vectorcraft"`), and the document counts as saved (as of the snapshot) once its file is written. Quit and Close wait for them. A job that fails reports the error in the status bar only (`ui.inspect` → `ui.status`), a path outside `--automation-write-root` included. With the preferences off (`prefs.set`), saves return once written. `app.save {path?, wait: true}` and `app.export {path, wait: true}` wait for the jobs already running, write the file before they reply whatever the preferences are set to, and return its result or the error. When the save asks first (the question before replacing a file that opened with losses, or on macOS and Linux the file dialog for an untitled document without `path`), the reply is `{pending}` or `"cancelled"` as before, and the save that runs after the answer uses the preferences. A `wait` that is not `true`, `false` or `null` is refused with "`wait` must be true or false", and nothing is written |
-| `engine.execute` `file.exportForScreens` | `{}` / `{…document.exportForScreens params}` | without params opens `exportForScreens` on the settings the document last exported with (`document.exportSettings`). While the Artboard tool is in use, the artboards it has selected (its `selected` option, the rows the Artboards panel highlights) are checked instead, and `select` is `range`, or `all` when every artboard is selected. Fields: `tab` (`artboards` \| `assets` \| `layers` \| `selection`; OK reads Export Layer or Export Selection on those), `layers` ([layer id…] checked), `selectionMode` (`one` \| `each`), `name` (the file name pattern of `document.exportForScreens`), `counterStart`, `folders` (`none` \| `rows` \| `format` \| `item` \| `itemFormat`), `exportPreset` (the preset applied last), `__savePreset` (the name typed to save one), `select` (`all` \| `range` \| `full`), `range` ("1-3, 5"), `boards` (a bool per artboard; checking them sets `select` and `range`), `includeBleed`, `folder` (desktop; default the Desktop, else home), `openLocation`, `subfolders`, `prefix`, `preset` (`""` \| `mobile` \| `density`), `formats` (rows `{format, scale: "2x" \| "100w" \| "100h" \| "72ppi", suffix, quality?, folder?}`), `settings` (`{png \| png8 \| jpg \| webp \| gif \| svg \| pdf: {…options}}`, the gear's Format Settings; `__settings` names the format shown). `ui.dialog.confirm` exports (a bad range or no folder keeps it open); on the web OK reads "Download" and the files download (several as one `.zip`). With params it runs `document.exportForScreens`: no `folder` returns the files (or with `zip: true` one store-only zip) as `dataBase64`; with `openLocation` the first file is shown in the file manager. When `warnings` is not empty, an export into a folder or a download shows the first in the status bar as Save As shows a save's notes |
+| `engine.execute` `file.exportForScreens` | `{}` / `{…document.exportForScreens params}` | without params opens `exportForScreens` on the settings the document last exported with (`document.exportSettings`). While the Artboard tool is in use, the artboards it has selected (its `selected` option, the rows the Artboards panel highlights) are checked instead, and `select` is `range`, or `all` when every artboard is selected. Fields: `tab` (`artboards` \| `assets` \| `layers` \| `selection`; OK reads Export Layer or Export Selection on those), `layers` ([layer id…] checked), `selectionMode` (`one` \| `each`), `name` (the file name pattern of `document.exportForScreens`), `counterStart`, `folders` (`none` \| `rows` \| `format` \| `item` \| `itemFormat`), `exportPreset` (the preset applied last), `__savePreset` (the name typed to save one), `select` (`all` \| `range` \| `full`), `range` ("1-3, 5"), `boards` (a bool per artboard; checking them sets `select` and `range`), `includeBleed`, `folder` (desktop; default the Desktop, else home), `openLocation`, `subfolders`, `prefix`, `preset` (`""` \| `mobile` \| `density`), `formats` (rows `{format, scale: "2x" \| "100w" \| "100h" \| "72ppi", suffix, quality?, folder?}`), `settings` (`{png \| png8 \| jpg \| webp \| gif \| svg \| pdf: {…options}}`, the gear's Format Settings; `__settings` names the format shown). `ui.dialog.confirm` exports (a bad range or no folder keeps it open); on the web OK reads "Download" and the files download (several as one `.zip`). With params it runs `document.exportForScreens`: no `folder` returns the files (or with `zip: true` one zip) as `dataBase64`; with `openLocation` the first file is shown in the file manager. When `warnings` is not empty, an export into a folder or a download shows the first in the status bar as Save As shows a save's notes |
 | Export for Screens' Assets tab, Asset Export panel | `ui.dialog.set` `tab: "assets"`, `assets: [asset id…]`; `window.panel {panel: "assetExport"}` | on the Assets tab of `exportForScreens` the `assets` field lists the checked asset ids (all of them when it opens); `ui.dialog.confirm` runs `document.exportForScreens {assets}` (nothing checked keeps it open) and OK reads "Export Asset". The Asset Export panel acts through `assets.*` and shares the format rows with the dialog (`assets.settings.set`) |
 | `engine.execute` `file.exportSelection` | `{multiple?}` | File › Export Selection…: collects the selected objects as one asset (`assets.add`; one per object with `multiple: true`) and opens `exportForScreens` on its Assets tab with just them checked → `{assets}`. `document.exportSelection` still exports the selection in one go, without the dialog |
 | CSS Properties panel | `window.panel {panel: "cssProperties"}`; `engine.execute` `css.copy` / `css.exportFile` | the panel shows `css.selection` of the selection (after Generate CSS, while nothing is selected, `css.generate`); its menu holds the options the commands take (`units`, `position`, `dimensions`, `unnamed`, `rasterize`). `css.copy {scope?, …options}` copies the CSS to the clipboard → `{css, rules}`; `css.exportFile {path?, scope?, …options}` writes `css.export` to `path` (else a picked file; the web downloads it) with the pictures of rasterized art next to it → `{path, rules, images, warnings}`, and the status bar shows the first of `warnings` as Export As shows an export's notes |

docs/mcp.md

@@ -3718,7 +3718,8 @@ slice ids and the ids of objects with an object slice.
 ## Export for Screens
 
 `document.exportForScreens` writes every chosen artboard (`range`, `artboards`; default all) in every format row
-into `folder`, or returns the files as `dataBase64` without one; `zip: true` packs them into one store-only `.zip`.
+into `folder`, or returns the files as `dataBase64` without one; `zip: true` packs them into one `.zip`,
+each file deflated, or stored when deflating does not make it smaller.
 A row is `{format, scale?}` where `scale` is a factor (`2`, `"2x"`), a pixel width (`"100w"` or `width: 100`), a
 height (`"100h"`) or a resolution (`"72ppi"`); raster rows name their files `@2x`, `@100w`… unless `suffix` says
 otherwise. `fullDocument` writes one file per row instead (a PDF of every artboard, other formats the bounds of all