Fix offline session recovery and add animated retry states

[Muawiya-contact]

Returning users can now open cached content while authentication refresh is delayed or offline. Unavailable screens show a consistent animated cloud and a Try again action, and authentication forms show clear connection advice instead of raw transport errors.

Closes #166. Closes #167.

• Restore the existing securely stored session for cached browsing; confirmed sign-out still clears account data and API requests still obtain tokens through Supabase.
• Bound stalled network requests to 15 seconds and retain actionable credential/confirmation messages.
• Add a shared offline state to Today, History, Saved, Stats, Personalization, and concept details. Preserve cached content, support reduced motion, and pause animation offscreen/in the background.
• Avoid substituting demo lessons or demo statistics when authenticated content is unavailable.

Validation: clean install, 10 regression tests (npm test, Node 24), npm run typecheck, and Android/web production exports passed. Browser checks with mocked services passed for expired-session cached browsing; uncached offline states in Today, History, Saved, Stats, and Personalization; topic/Today/detail recovery after reconnecting; dark theme with reduced motion; and friendly offline sign-in errors. No uncaught browser errors occurred. Physical-device validation is still needed; no live backend or production data was used.

This PR targets develop and preserves its individual commits. App version and native runtime are unchanged. After merge, release preparation can add the version bump and eligible one-time What's New entry before the develop to main PR.

[Muawiya-contact]

Ok