feat(engine): add faction system for social emergence

- Add Factions model (optimists/fearful/neutral)
- Implement classify_faction() based on stance thresholds
- Add update_factions() to track faction distribution
- Add apply_faction_influence() for faction→mood feedback
- Integrate faction system into tick flow

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

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

engine-python/app/engine.py

@@ -7,6 +7,7 @@ from .models import (
 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
 
 MAX_EVENTS = 20
 MAX_MEMORY_PER_AGENT = 3
@@ -90,6 +91,12 @@ def process_events(state: WorldState, events: List[Event]) -> WorldState:
     # 应用社交影响
     apply_social_influence(state)
 
+    # 更新派系分布
+    update_factions(state)
+
+    # 派系影响世界情绪
+    apply_faction_influence(state)
+
     return state
 
 
@@ -126,6 +133,12 @@ def check_and_trigger_global_event(
         # 应用社交影响
         apply_social_influence(state)
 
+        # 更新派系分布
+        update_factions(state)
+
+        # 派系影响世界情绪
+        apply_faction_influence(state)
+
         result = GlobalEventResult(
             triggered=True,
             event=global_event.to_info()