LRC-LIB-LIBFOLDERS: Synchronize Folder says a folder is up to date, with one Close

When the scan finds nothing to import, relink, remove or read, the dialog
showed four greyed choices (two still ticked) and a Synchronize button
that started an empty job with an activity row. It now shows the folder,
"The library is up to date with this folder." and any Skipped lines, with
one Close and no Cancel (`only_shows`). `sync::confirm` answers
`{"upToDate": true}` and starts nothing, so `ui.dialog.confirm` and agents
get the same result.

Co-Authored-By: Claude <noreply@anthropic.com>

docs/control-protocol.md

@@ -76,7 +76,7 @@ filmstrip is visible.
 | `ui.scroll` | `{dx, dy, cmd?, ctrl?, shift?, alt?}` | Wheel / two-finger scroll at the current pointer; pans over the image, modifier-scroll zooms |
 | `ui.zoom` | `{factor}` | Pinch zoom at the current pointer (positive scale multiplier; 1 = unchanged). Position it first with `ui.move` or `ui.hoverWidget` |
 | `ui.set` | partial UI state, e.g. `{"view": "detail"}` | Resulting UI state |
-| `ui.dialog.confirm` / `ui.dialog.cancel` | — | Close the open dialog |
+| `ui.dialog.confirm` / `ui.dialog.cancel` | — | Close the open dialog (confirm runs its action; Synchronize Folder on a folder that is up to date answers `{"upToDate": true}` and starts nothing) |
 | `ui.resize` | `{width, height}` | Resize the window |
 | `ui.zoomFactor` | `{factor}` | Set the interface scale (0.5–3; egui's zoom keys are off, Cmd+= / Cmd+- zoom the photo) |
 | `ui.screenshot` | `{path?, headless?}` | `{path, width, height}` once the frame (with finished renders) is captured. `headless: true` draws the UI on the CPU (no compositor needed); a windowed capture that gets no frame within 2 s falls back to headless automatically. While the loupe still waits for a render, `ui.widgets {filter: "loupe:rendering"}` lists its "Rendering…" pill; `loupe:renderFailed` is the pill saying a render failed behind a stand-in; Compare and Reference panes have their own (`compare:rendering:<pane>`, `compare:renderFailed:<pane>`) |