Fix #3797: documents open in Preview, and Outline is a setting of each document

View > Outline was one app-wide flag saved in the interface preferences,
so after Cmd+Y every later launch drew every opened or new document as
outlines, with no fills. The flag is now part of each document's view:
a document opens in Preview, each tab shows its own Outline or Preview,
and the setting is not saved at launch. An older preferences file that
holds the flag still loads, and its value is ignored.

The Outline command and ui.set's outline act on the active document and
are an error without one.

docs/control-protocol.md

@@ -101,7 +101,7 @@ the two can still win that race.
 | `ui.move` | `{x, y}` | screen-point pointer move |
 | `ui.click` / `ui.drag` | `{x, y, button?, count?, shift?, alt?, ctrl?, cmd?}` / `{x, y, toX, toY, steps?, count?, button?, shift?, alt?, ctrl?, cmd?}` | egui pointer input; see synthetic input budgets above |
 | `ui.wheel` | `{x, y, dy?, dx?, unit?: "line"\|"point", shift?, alt?, cmd?}` | a mouse wheel turn over screen point (x, y): `dy` notches up (+) or down, `dx` sideways. Over the canvas the wheel scrolls and Cmd- or Alt-wheel (Option on the Mac) zooms about the pointer; with the `zoomWithMouseWheel` preference the wheel and Alt-wheel zoom about the pointer, Shift-wheel scrolls up and down and Cmd-wheel (Ctrl on Windows and Linux) sideways. Over a focused numeric field (click it first) each notch steps its value as Up/Down do (Shift: ten, Cmd/Ctrl: a tenth) and the panel stays put; over anything else in a panel the wheel scrolls it |
-| `ui.set` | `{brightness?, panel?, rulers?, outline?, grid?, smartGuides?, boundingBox?, controlBar?, imageTracePreview?}` | `imageTracePreview`: the Image Trace panel's Preview (`ui.inspect` shows it as `ui.image_trace_preview`) |
+| `ui.set` | `{brightness?, panel?, rulers?, outline?, grid?, smartGuides?, boundingBox?, controlBar?, imageTracePreview?}` | `outline`: View › Outline for the active document only (each document has its own, a document opens in Preview, and `ui.inspect` shows it as `view.outline`; an error without a document). `imageTracePreview`: the Image Trace panel's Preview (`ui.inspect` shows it as `ui.image_trace_preview`) |
 | `ui.dialog.set` / `.confirm` / `.cancel` | `{field, value}` or `{fields: [{field, value}…]}` | fill and submit the open dialog. `ui.dialog.set` takes the fields the dialog has (`ui.inspect`), `__` fields, `discard` on a dialog with a discard button, `preview` on one with a live preview, the fields that the dialog reads but adds only when a control changes (such as `searchFolder`, or `copy` in the Transform dialogs), and the fields it passes to the command it runs: every parameter of the `command` dialog's command (`ui.paramDialog`), and the `textureImage` that Load Texture… sets in the Glass and Texturizer effects; any other field is an error that lists the dialog's fields, and the dialog stays as it was `fields` sets the list (at most 256 items) in order (a missing `value` is `null`) and checks every item first: when one is refused, the call is an error and no field changes |
 | `ui.screenshot` | `{path?, data?}` | capture the window (PNG), written to `path`; `data: true` sends it back as `pngBase64` too. The inline PNG is capped at 64 MiB: with a `path` the file is still written and `pngBase64` is omitted when the image is larger, while a path-less `data: true` request fails if either the raw RGBA image or the encoded PNG exceeds the cap. Needs a presented frame: with the screen locked or the window minimized/covered it fails after ~8 s with an explanatory error |
 | `ui.render` | `{path?, scale?, artboard?, data?, traceViews?}` | render an artboard headlessly (PNG with the pixels of `app.export {format: "png", background: "white"}` at the same scale; `artboard`: its 0-based index, default the first; `traceViews: true`: Image Trace objects draw in their View, as on the canvas, instead of their tracing result): written to `path`, else (or with `data: true` as well) sent back as `pngBase64` |