feat: implement AI Director & Narrative Voting System (Phase 9)

Add complete AI Director system that transforms the survival simulation
into a user-driven interactive story with audience voting.

Backend:
- Add DirectorService for LLM-powered plot generation with fallback templates
- Add VoteManager for dual-channel voting (Twitch + Unity)
- Integrate 4-phase game loop: Simulation → Narrative → Voting → Resolution
- Add vote command parsing (!1, !2, !A, !B) in Twitch service
- Add type-safe LLM output handling with _coerce_int() helper
- Normalize voter IDs for case-insensitive duplicate prevention

Unity Client:
- Add NarrativeUI for cinematic event cards and voting progress bars
- Add 7 new event types and data models for director/voting events
- Add delayed subscription coroutine for NetworkManager timing
- Sync client timer with server's remaining_seconds to prevent drift

Documentation:
- Update README.md with AI Director features, voting commands, and event types

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/schemas.py

@@ -66,6 +66,15 @@ class EventType(str, Enum):
     VFX_EVENT = "vfx_event"              # Visual effect trigger
     GIFT_EFFECT = "gift_effect"          # Twitch bits/sub effect
 
+    # AI Director & Narrative Voting (Phase 9)
+    MODE_CHANGE = "mode_change"          # Game mode transition
+    NARRATIVE_PLOT = "narrative_plot"    # Director generated plot point
+    VOTE_STARTED = "vote_started"        # Voting session started
+    VOTE_UPDATE = "vote_update"          # Real-time vote count update
+    VOTE_ENDED = "vote_ended"            # Voting closed
+    VOTE_RESULT = "vote_result"          # Final voting result
+    RESOLUTION_APPLIED = "resolution_applied"  # Plot resolution executed
+
 
 class GameEvent(BaseModel):
     """