feat: 添加观点传播系统

- 新增 Stance 数据结构 (optimism/fear)
- 情绪影响 stance (happy→乐观, anxious→恐惧)
- 实现 apply_social_influence 社交影响函数
- 确定性随机选择接触对象
- 单次变化限制 ±0.1

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

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

engine-python/app/state.py

@@ -1,6 +1,6 @@
 import json
 from pathlib import Path
-from .models import WorldState, AgentState, GlobalMeter
+from .models import WorldState, AgentState, GlobalMeter, Stance
 
 STATE_FILE = Path(__file__).parent.parent / "state.json"
 
@@ -12,8 +12,18 @@ def get_default_state() -> WorldState:
         weather="sunny",
         town_mood=0,
         agents={
-            "alice": AgentState(emotion="calm", goal="探索小镇", memory=[]),
-            "bob": AgentState(emotion="calm", goal="与人交流", memory=[]),
+            "alice": AgentState(
+                emotion="calm",
+                goal="探索小镇",
+                memory=[],
+                stance=Stance(optimism=0.6, fear=0.4),
+            ),
+            "bob": AgentState(
+                emotion="calm",
+                goal="与人交流",
+                memory=[],
+                stance=Stance(optimism=0.4, fear=0.6),
+            ),
         },
         events=[],
         global_meter=GlobalMeter(value=0, threshold=100, cooldown=0),