fix(tv): restore imports, UI mode selection, and channel navigation

[PastaHimself]

Summary

Fixes the remaining Android TV regressions from the tv-stuff feedback pass:

• adds a TV-native Import Data route using Android's system document picker
  • Flow backup JSON
  • master backup ZIP
  • YouTube subscription OPML/XML
  • NewPipe subscriptions JSON
  • LibreTube subscriptions JSON
  • YouTube Takeout ZIP
• adds a shared OPML/XML subscription parser/importer for canonical YouTube channel feeds, including XML entity decoding and duplicate-channel suppression
• fixes Settings → UI mode jumping back to the first settings category when selecting Mobile or TV by removing the forced focus clear/frame delay
• makes the channel name in the TV video overlay actionable and routes to the existing TV channel screen so users can open the channel and subscribe

Regression coverage

• OPML parser tests cover YouTube feed outlines, XML entities, duplicate channel IDs, unsupported feeds, and non-XML input
• TV regression guards fail unit CI if the forced focus clear/frame wait is reintroduced or the player → channel route/button is removed

Sync findings

The two reported device-sync failures are already addressed in the current tv-stuff base and are intentionally not reworked in this PR:

• recommendation/FlowNeuro sync already emits the desktop-compatible bare G-counter map rather than the old perDevice wrapper that caused invalid-JSON/type failures
• followed channels already sync through the dedicated subscribed_channels collection independently from subscription groups, so subscriptions no longer depend on groups existing

Existing regression coverage for those sync paths remains in place.

Validation

• based on current tv-stuff HEAD (cf2e0cea19933a54aab29e9ef39daffeb6ce9b36)
• GitHub Actions is the authoritative Android validation because the local runtime cannot resolve the Gradle distribution host
• current head validation is running on the CI-only main-target PR ci(tv): validate tv-stuff fixes #8

Base: tv-stuff
Head: fix/tv-stuff-feedback