feat: add cursor auto-hide feature with configurable idle delay

[j4rviscmd]

Summary

• Add cursor auto-hide feature that hides the mouse cursor after a configurable period of inactivity
• Settings are persisted across app restarts and take effect immediately without restarting
• Interactive overlays (dialogs, menus, dropdowns, BlockNote toolbars) always keep the cursor visible

Changes

New files

• src/features/editor/lib/cursorAutoHideConfig.ts — defaults, mutable config object, store keys, CSS class name, always-visible selectors
• src/features/editor/hooks/useCursorAutoHide.ts — two hooks:
  • useCursorAutoHide: settings UI hook (reads/writes configStore, updates cursorAutoHideConfig)
  • useCursorAutoHideEffect: effect-only hook (registers global mousemove/mouseover listeners, reads cursorAutoHideConfig directly so changes take effect without re-render)
• src/features/settings/ui/CursorAutoHideOption.tsx — settings UI (toggle + 1–30 s delay slider)

Modified files

• src/features/editor/index.ts — export both hooks
• src/features/settings/ui/SettingsDialog.tsx — add CursorAutoHideOption section
• src/App.tsx — call useCursorAutoHideEffect() for app-lifetime mouse listeners
• src/index.css — add html.cursor-autohide-hidden CSS rules

Design decisions

The hook is split into two (useCursorAutoHide + useCursorAutoHideEffect) to avoid the dual-instance problem: if a single hook managed both settings and listeners, the settings dialog component would register its own listener set that gets destroyed when the dialog closes. By keeping listeners in useCursorAutoHideEffect (called once in App.tsx) and sharing state via the cursorAutoHideConfig mutable object, settings changes from the UI propagate to the effect without any re-render or restart.