feat(engine): add faction power system with event triggers

- Add FactionData model with power and members fields
- Add FactionEventResult model for faction event responses
- Add faction field to AgentState
- Implement faction classification based on emotion
- Add faction event triggers (festival/panic) when power >= 5
- Update StepResponse to include triggered_faction_event
- Add tests for new faction system

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

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

engine-python/app/engine.py

@@ -2,12 +2,14 @@ from __future__ import annotations
 from typing import List, Optional, Tuple
 from .models import (
     WorldState, AgentState, Event, Action, Emotion, Weather,
-    GlobalEventResult, GlobalEventInfo
+    GlobalEventResult, GlobalEventInfo, FactionEventResult
 )
 from .global_events import GLOBAL_EVENT_POOL, GlobalEvent
 from .opinions import generate_opinions
 from .social_influence import apply_social_influence
-from .factions import update_factions, apply_faction_influence
+from .factions import (
+    update_factions, apply_faction_influence, check_and_trigger_faction_event
+)
 
 MAX_EVENTS = 20
 MAX_MEMORY_PER_AGENT = 3