Adopt Angular signals for reactive state

[dcaslin]

Summary

• Convert AppStateService BehaviorSubjects to WritableSignal (6 fields: disableAds, debugmode, favoritesList$, favoritesMap, hiddenMilestones, hiddenClanMilestones)
• Convert ChildComponent.loading from BehaviorSubject to signal(false)
• Convert loading BehaviorSubjects to signals in 7 services/components (StreamingService, GearService, ClanStateService, FriendStarComponent, PerkbenchComponent, DimSyncService, MarkService)
• Update 54 templates: replace field | async with field() signal reads
• Replace .next() with .set() and .getValue() with () across 24 TS files
• Remove AsyncPipe import from 11 components that no longer use it
• Convert FriendsComponent.members to signal, use effect() for reactive derivation from favoritesList$
• Version bumped to 29.4.0

What stays as Observable

• PlayerStateService (complex: private subjects + public .asObservable() pattern)
• ClanStateService non-loading subjects (many BehaviorSubjects with rich usage)
• GearFilterStateService observables
• All HTTP/streaming observables

Verification

• ng build — clean ✅
• ng build --configuration production — 2.98 MB initial bundle ✅
• npm run lint — 0 errors ✅

Test plan

• CI build passes
• Smoke test: home page, player profile, gear manager, clan pages, friends list
• Verify loading spinners still appear/disappear correctly
• Verify debug mode toggle works (settings → all pages showing debug info)
• Verify friend star add/remove updates correctly

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