Add PWA quick-resume surfaces for the current book

[mokhov]

Problem

An installed reader still requires navigating through the application before returning to the current book.

Proposed behavior

Use supported PWA and operating-system surfaces to resume the latest book directly and show its identity where privacy permits.

Acceptance criteria

• Investigate manifest shortcuts, notifications, media-session artwork, and supported install surfaces.
• Every shortcut opens the correct book at its stable saved anchor.
• Current-book titles or covers are exposed outside the app only after an explicit privacy choice.
• Unsupported platforms receive a clean in-app Continue Reading fallback.
• The implementation does not delay startup or reveal stale loading controls.