feat(app): add reactive pet bubbles based on global metrics

[aiexkwan]

Summary

• Pet reacts to 6 global metrics via speech bubbles: rate limit, daily token usage, session count, hunger, streak days, and daily meals
• Powered entirely by existing @Published data sources (OpenUsageClient, PetCareController, AppDaemon) — zero new extraction logic
• Tiered phrase pools (silent → low → mid → high) with cooldown tracking (same-metric ≥10min, cross-metric ≥30s, hunger max 2/day) to prevent notification spam
• New "Pet Reactive Bubbles" toggle in Settings → Bubble (default ON)
• 36 unit tests covering all threshold boundaries and cooldown gate logic

Design details

Component	Implementation
ReactiveEngine	@MainActor singleton, Combine sinks on 3 existing publishers
Thresholds	Static constants in Thresholds namespace, table-driven tier resolution
Cooldown	Per-metric + cross-metric + hunger daily limit, UTC day-key tracking
UI integration	PetController.flashReactiveLine(_:) — respects showChat, never changes pet mood
Settings	BubbleSettings.reactiveBubblesEnabled persisted in UserDefaults

Test plan

• swift build — compiles cleanly
• swift test — 186 tests, 0 failures, no regressions
• Manual: wait for rate limit to drop below 50% → pet shows rate limit reaction bubble
• Manual: accumulate >1M tokens in a day → pet shows token usage reaction
• Manual: open 5+ concurrent agent sessions → pet shows session count reaction
• Manual: toggle OFF "Pet Reactive Bubbles" in Settings → no more reactive bubbles appear
• Manual: toggle OFF "Show chat" → reactive bubbles also suppressed