feat(backend): T1.3 月报管理 CRUD — 列表/详情/创建/更新/提交/删除

- 路由：GET/POST/PUT/DELETE /api/v1/reports + POST /reports/{id}/submit
- 状态机：draft → submitted → ai_parsed → reviewed
- 防重复：同年同月同企业不可重复创建
- 租户隔离：通过 company 关联校验
- 测试：7 个月报测试（总计 33 tests passed）

backend/app/schemas/report.py

@@ -0,0 +1,52 @@
+"""月报相关 Pydantic schema。"""
+
+from datetime import datetime
+from pydantic import BaseModel, Field
+
+
+class MonthlyReportCreate(BaseModel):
+    """创建月报请求。"""
+
+    company_id: str
+    period_year: int = Field(..., ge=2020, le=2100)
+    period_month: int = Field(..., ge=1, le=12)
+    raw_content: str | None = None
+
+
+class MonthlyReportUpdate(BaseModel):
+    """更新月报请求。"""
+
+    raw_content: str | None = None
+    status: str | None = Field(default=None, description="draft/submitted/ai_parsed/reviewed")
+    structured_data: dict | None = None
+    ai_summary: str | None = None
+    ai_concerns: dict | None = None
+
+
+class MonthlyReportResponse(BaseModel):
+    """月报信息响应。"""
+
+    id: str
+    company_id: str
+    period_year: int
+    period_month: int
+    status: str
+    raw_content: str | None = None
+    structured_data: dict | None = None
+    ai_summary: str | None = None
+    ai_concerns: dict | None = None
+    submitted_by: str | None = None
+    submitted_at: datetime | None = None
+    reviewed_by: str | None = None
+    reviewed_at: datetime | None = None
+    created_at: datetime
+    updated_at: datetime
+
+
+class MonthlyReportListResponse(BaseModel):
+    """月报列表响应。"""
+
+    items: list[MonthlyReportResponse]
+    total: int
+    page: int
+    page_size: int