Polish: ContentType enum consistency + PulsingLiveDot + minor idiom cleanups

[Yokomoko]

Catch-all for the smaller cleanups flagged in the review. Each is independently trivial but they share the theme of "tidy while in the neighbourhood".

From various: architect.md #13, quality.md #10, #11, #12, idioms.md #6, #7, perf.md #12, #15

• ContentType enum: ContentType.kt exists but every DB/UI site uses raw "live"/"movie"/"show" strings. Add .dbValue and roll out. (arch 'More Like This' rail on detail screens #13, quality Background sync via WorkManager #10)
• PulsingLiveDot: rememberInfiniteTransition fires a 800ms scale animation every frame while Live tab visible — 3 concurrent animation sources on the screen. Switch to RepeatMode.Reverse with 1200ms cycle, or replace scale with alpha pulse. (perf Audio track selection (multi-language) #12)
• EpgChannelMatcher mutable state: has var totalResolved, var totalMissed, val loggedMisses = mutableSetOf() mutated on every resolve() — not thread-safe if called concurrently. Move diagnostic counting out or use AtomicInteger. (quality Favourite channel zapping (Sky-style) #11)
• M3uParser.currentExtinf!! after null-check: smart-cast blocked by mutable var. Copy to local val or use let block. (quality Audio track selection (multi-language) #12)
• HomeViewModel.isInWatchlist() redundant: uses .first() on a Flow while watchlist: StateFlow already exists on the same VM. Delete and have callers check watchlist.value. (idioms Last-watched channel memory #6)
• Two LaunchedEffect(Unit) in Shell.kt for unrelated effects: replace with named keys like LaunchedEffect("splashTimeout") and LaunchedEffect("initialFocus"). (idioms Stream error recovery (auto-retry) #7)
• Shell.kt holds second HomeViewModel subscription just for splash dismiss. Move the "first data arrived" signal into EnrichmentProgressTracker or a dedicated SplashViewModel. (perf Search result poster thumbnails #15)