feat(backend): T1.2 企业档案 CRUD — 列表/详情/创建/更新/删除

- 路由：GET/POST/PUT/DELETE /api/v1/companies
- 支持分页、关键词搜索、行业/阶段筛选
- 租户隔离：只能操作本租户企业
- 测试：11 个企业 CRUD 测试，全部 passed（总计 26 tests）

backend/app/schemas/company.py

@@ -0,0 +1,54 @@
+"""企业相关 Pydantic schema。"""
+
+from datetime import datetime
+from pydantic import BaseModel, Field
+
+
+class CompanyCreate(BaseModel):
+    """创建企业请求。"""
+
+    name: str = Field(..., min_length=1, max_length=200)
+    industry: str | None = Field(default=None, max_length=100)
+    stage: str | None = Field(default=None, max_length=50)
+    logo_url: str | None = Field(default=None, max_length=500)
+    description: str | None = None
+    total_funding: str | None = Field(default=None, max_length=50)
+    website: str | None = Field(default=None, max_length=500)
+
+
+class CompanyUpdate(BaseModel):
+    """更新企业请求。"""
+
+    name: str | None = Field(default=None, min_length=1, max_length=200)
+    industry: str | None = Field(default=None, max_length=100)
+    stage: str | None = Field(default=None, max_length=50)
+    logo_url: str | None = Field(default=None, max_length=500)
+    description: str | None = None
+    total_funding: str | None = Field(default=None, max_length=50)
+    website: str | None = Field(default=None, max_length=500)
+
+
+class CompanyResponse(BaseModel):
+    """企业信息响应。"""
+
+    id: str
+    tenant_id: str
+    name: str
+    industry: str | None = None
+    stage: str | None = None
+    logo_url: str | None = None
+    description: str | None = None
+    founded_at: datetime | None = None
+    total_funding: str | None = None
+    website: str | None = None
+    created_at: datetime
+    updated_at: datetime
+
+
+class CompanyListResponse(BaseModel):
+    """企业列表响应。"""
+
+    items: list[CompanyResponse]
+    total: int
+    page: int
+    page_size: int