refactor(subscriptions): restructure the screen, share its components, and adopt expressive controls

[A-EDev]

Summary

Splits the 1,309-line subscriptions screen into nine focused files and moves its shared pieces out: one subscribe button now backs the channel page, the player and the manager, and one expressive pull-to-refresh backs every refreshing surface. Adopts M3 Expressive controls on the way, fixes the missing refresh progress bar, and adds channel groups to the channel page.

Related issue

Closes #995
Closes #982

Change type

• Bug fix
• Feature
• Refactor or maintenance
• Build, packaging, or CI
• Documentation

Validation

• ./gradlew :app:assembleGithubDebug
• ./gradlew :app:testGithubDebugUnitTest
• I ran any additional flavor-specific build or test tasks affected by this change.
• I manually tested the affected behavior on an Android device or emulator.

Also run and passing: ./gradlew spotlessCheck, :app:compileGithubDebugKotlin, :app:compileFossDebugKotlin.

Test device and Android version: Xiaomi POCO X6 Pro, HyperOS 3.0.9.0, Android 16

Two crashes were found on device during testing and are fixed here: ButtonGroup throwing from its measure policy under a tight width constraint, and the groups dialog painting rows over the dialog container. The performance changes below are structural — they have not been measured with a profiler.

Screenshots or recordings

Risk and compatibility

Fixes

• [Bug]: Subscription feed refresh progress bar isn't showing #995 — the refresh progress bar was gated on isLoading, which the launch refresh deliberately leaves false so the pull indicator does not spin on every start. The channel counts were always published, so the bar now follows those instead. Regression from 2.2.0.
• [Feature]: Being able to add to channel groups directly from the channel tab #982 — groups can be added and removed from the channel page via the subscribe menu, reusing the existing SaveToCollectionSheet.
• Subscription avatars went through a raw AsyncImage, skipping ThumbnailUrlResolver and the placeholder fallback that every other avatar in the app uses.
• An always-true || true guard, an unreachable selected-avatar branch holding hardcoded Color.Black/Color.White, and context.getString inside composition.
• Captured logs were flooded by BLASTBufferQueue/HWUI frame spam; those tags are now silenced through logcat's filterspec, and the per-channel failure reason is recorded when the fetch fails rather than scraped back out of logcat.

Behaviour changes worth knowing about

• SubscriptionsViewModel is now activity-scoped on phone (sharedSubscriptionsViewModel()), matching what the TV shell already did. A tab visit no longer builds a fresh instance whose ensureStarted() restarts five collectors and another feed refresh, and feed and scroll state now survive tab switches.

• Two refresh timers are now gated. The 60 s relative-time tick suspends while nothing observes the feed state, and the 3-minute stale poll runs only while RESUMED. The tick re-maps, filters and sorts the whole feed, so it was not a cheap clock update.

• The subscribe button is a split button when subscribed — the leading half toggles notifications, the trailing half opens the menu. It replaces three implementations, two of which were both named SubscribeButton. Shorts and TV keep their own.

• New preference show_channel_group_badges, off by default. With it off the group table is never observed at all.

• SubscriptionGroup moved from ui/screens/subscriptions/ to data/model/, so the channel page can use it without importing another feature's screen package.

• Two new fields on existing data classes (failedChannelReasons on the refresh progress and UI state). No entity or schema change.

• 4 new strings in values/strings.xml. Other locales are left to Weblate.

• The change does not introduce secrets, private data, or unexpected telemetry.

• New user-facing text uses Android string resources.

• Dependency and lockfile changes are intentional and limited to this PR.

• Room schema changes include the required version bump and migration, or this PR does not change the Room schema.

• Breaking changes and upgrade steps are clearly documented.

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