feat: announce the logical focus and states to Narrator

[nextestudios]

Summary

• The XAML focus stays on the window root while the logical focus lives in AppController, so Narrator used to hear nothing when the controller moved the focus. Now:
  • AppController.DescribeFocus() (Application, testable) says where the focus is and what is focused. The context covers home, folder, archive, search results, recycle bin, menus, dialogs (title, lines, message), the on-screen keyboard, the controller wizard, the path bar and tabs. The item gets name, type, size, "N de M" and states in words: marcado, recortado, bloqueado: motivo, com senha, oculto, and indisponível: motivo for menu items and keys.
  • TakeAnnouncement() returns the full context only when it changes and just the item while moving inside it. Nothing is repeated.
  • MainWindow raises a UI Automation notification (ImportantMostRecent) for each announcement, mirrors it in the root's automation name (so Caps+Tab repeats it) and makes the status line a polite live region. Bottom-bar messages are read without moving the focus.
• Existing per-element names (rows, tiles, breadcrumbs, tabs, keys, prompts) stay as they are. Type/size texts now come from one helper (EntryText) shared by rows and announcements.
• The app uses no sound or vibration; every state is already text plus a shape, and now also speech.

Tests

• CI: ScreenReaderJourneyTests walks home → folder → mark → cut → menu with a disabled item → back → exit dialog and asserts exactly what would be announced, including that an unchanged state announces nothing.
• Manual (docs/TESTING.md, "Narrador (enhancement: screen reader (Narrator) support pass #40)"): real Narrator with a controller across list, grid, menus, dialogs, keyboard, path bar, tabs and bottom-bar messages. These can't run in CI.

Closes #40

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