feat: 后端 CRUD 完成（episodes + yearly_targets + users 管理 API）

backend/app/schemas/yearly_target.py

@@ -0,0 +1,31 @@
+"""
+年度收视目标 Schema — 请求 / 响应模型
+
+业务规则：yearly_targets 只增不改，ON CONFLICT DO NOTHING
+"""
+
+from datetime import date
+
+from pydantic import BaseModel, ConfigDict
+
+
+class YearlyTargetBase(BaseModel):
+    year: int
+    base_target: float
+    stretch_target: float
+    issued_date: date | None = None
+    notes: str | None = None
+
+
+class YearlyTargetCreate(YearlyTargetBase):
+    pass
+
+
+class YearlyTargetUpdate(YearlyTargetBase):
+    pass
+
+
+class YearlyTargetResponse(YearlyTargetBase):
+    id: int
+
+    model_config = ConfigDict(from_attributes=True)