Add OPDS catalogs with feed caching and persistent import tracking

[Eoic]

Ticket

User-requested OPDS catalog support and book-details refinements.

Summary

Readers can browse OPDS catalogs, search and paginate through feeds, choose a book format, and import books through the backend relay. Catalogs remain usable without signing in, and successful imports stay linked to their library books across restarts.

• Add OPDS 1/2 parsing, catalog and credential management, routed publication details, download progress, cancellation, retry, and mobile swipe actions.
• Cache feeds and covers by account and catalog, show saved feeds during revalidation, and retain usable content when offline. Catalog, credential, and account changes invalidate the appropriate cached state.
• Persist exact publication/acquisition-to-library mappings, offer Open book for existing imports, and update ownership after library deletion.
• Unify catalog and library details: mobile app bars and sticky tabs, cover placeholders, buttons, metadata sections, compact progress, and aligned tab content. Refresh feedback stays inside the refresh button without shifting the list.
• Refine sheets, pagination, navigation counts, and browser history; prevent duplicate web engine initialization after a terminal hot restart.

Testing

From app/:

• flutter test --no-pub --reporter expanded: 1,371 passed, 19 skipped.
• dart format --output=none --set-exit-if-changed .: 431 files checked, no changes.
• flutter analyze --no-pub: no issues.
• node --test test/web/flutter_bootstrap_test.cjs: 4 passed.
• flutter build web --no-pub: passed.

Regression coverage includes account isolation, stale async operations, cache invalidation, persistent ownership, route history, mobile tab pinning, and stable list/grid positions during refresh.

UI evidence

Reviewed generated screenshots from test/opds/layout_test.dart for mobile and desktop layouts, dark/light/e-ink themes, and enlarged text. Captures are generated locally under app/build/catalog-review/ and are not committed.

Compatibility and migration

Requires the anonymous OPDS relay already on the server's default branch: PapyrusReader/server@bfc4fbc.

No database migration is required. Feed caching and import provenance are local and scoped to the active account/catalog. Existing library books without OPDS provenance are not matched by title or author.

Notes

Review docs/opds-support.md for supported acquisition methods, relay behavior, caching, and ownership matching. Unsupported acquisition methods remain visible in the format sheet but cannot be imported on the current device.

Checklist

• The branch, commits, and pull request title follow the repository conventions.
• The change is complete and limited to the ticket's scope.
• Relevant tests have been added or updated.
• Formatting, analysis, and tests pass.
• Documentation, UI evidence, and migration notes are included where relevant.
• No credentials, personal data, copyrighted fixtures, or unrelated generated files are included.
• The branch is up to date with its target branch.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.