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/models.py

@@ -38,6 +38,12 @@ class Opinion(BaseModel):
     tick: int   # 生成时的 tick
 
 
+class Stance(BaseModel):
+    """角色立场"""
+    optimism: float = Field(default=0.5, ge=0.0, le=1.0)
+    fear: float = Field(default=0.5, ge=0.0, le=1.0)
+
+
 class AgentState(BaseModel):
     emotion: Emotion = Emotion.CALM
     goal: str = ""
@@ -45,6 +51,8 @@ class AgentState(BaseModel):
     opinion: Optional[Opinion] = None
     # 记录已评论过的事件，防止重复生成
     commented_effects: List[str] = Field(default_factory=list)
+    # 角色立场
+    stance: Stance = Field(default_factory=Stance)
 
 
 class WorldState(BaseModel):