Keep panels still as the macOS menu bar and Dock show and hide

[enaboapps]

Closes #1023.

Cause

Panels are placed inside NSScreen.visibleFrame. That area leaves out the menu bar and Dock only while they currently show. In a full-screen app, or with either set to hide automatically, they show only while the pointer is at the top or bottom edge.

settle_environment reads the work area on every update while a panel is open:

• The mouse panel was given the new area each time.
• The keyboard refitted whenever the area changed.

So both jumped every time a bar slid in or out. Near an edge, that repeated as flicker.

Change

On macOS (WORK_AREA_FOLLOWS_AUTO_HIDE), panels read the work area again only when the active Space changes. That happens when entering or leaving a full-screen app, or choosing another desktop.

• Space tracking: macos.rs observes NSWorkspaceActiveSpaceDidChangeNotification and calls point_scan_runtime::space_changed(). That bumps a counter and starts a 1 s settling window.
• Area policy: the pure helper steady_area keeps the environment's area while the Display and the Space are both unchanged and nothing is settling. Otherwise it uses the fresh work area. After settling, settle_environment records the Space the area belongs to.
  • The mouse panel and the keyboard refit both go through steady_area.
  • Point scanning ignores the work area, but it refreshes the area for a keyboard it may open whenever the Space changes.
• validate_display: on macOS it skips the work-area comparison explicitly, since the area is kept current per Space instead.
• Still refits straight away: another display, or the same display with a different position, size or scale.
• Windows unchanged: the flag is off there, and an auto-hidden taskbar never changes the work area.

Trade-off: moving the Dock or changing its size without changing Space takes effect the next time the panel opens or the Space changes. Until then, a panel may overlap the Dock. Panels sit above the menu bar and Dock (screen-saver level) and never take clicks, so the overlap is visual only.

Docs updated in point-scan.md, qwerty-keyboard.md and scanner-architecture.md.

Validation

• npm run prediction-model, npm run lint, npm test (294 passed), npm run build
• cargo fmt --check, cargo clippy --all-targets -D warnings, cargo test (748 passed)
• New tests:
  • panels_keep_their_area_while_auto_hidden_bars_show_and_hide: area kept on the same Space; followed after a Space change and while settling; followed on Windows; refitted for another or resized display.
  • a_space_change_is_counted_and_settles.
• The macOS-only observer can't be compiled on the Windows dev machine, because the cross-check needs a C toolchain. CI's macOS build covers it.
• Needs checking on a Mac (npm run macos:run):
  1. Open the keyboard and the mouse panel in a full-screen app. Move the pointer to the top and bottom edges: the panels should stay still.
  2. Leave full screen with the keyboard open: it should refit above the Dock within about a second.
  3. Repeat on a normal desktop with the menu bar and Dock set to hide automatically.

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