refactor(db): 统一数据库 schema — 软删除、命名规范、约束标准化

- 全表新增 deleted_at 列，统一软删除替代硬删除+archived_at
- models.model_id 重命名为 external_id，消除语义混淆
- conversations.model_id 改为可空（模型为建议而非绑定）
- messages 新增 updated_at，移除 CASCADE 改为 DAO 层级联
- 移除 DB 层 UNIQUE 约束，改为应用层检查（配合软删除）
- 新增 helpers.ts（baseColumns + 构造层防御）、ESLint 规则、契约测试
- 迁移 0004 补全 CHECK 约束（providers.type/materials.status/messages.role）
- DAO 层全面重写：级联软删除、应用层唯一、provider 删除保护
- 路由/前端/测试全量适配 externalId 重命名及类型变更

tests/web/routes/projects.test.tsx

@@ -11,7 +11,6 @@ import { ProjectTable } from "../../../src/web/features/projects/components/Proj
 import { installFetchMock, jsonResponse, mockMetaResponse, renderWithProviders } from "../test-utils";
 
 const ACTIVE_PROJECT: Project = {
-  archivedAt: null,
   createdAt: "2024-01-01T00:00:00.000Z",
   description: "活跃描述",
   id: "p1",
@@ -21,7 +20,6 @@ const ACTIVE_PROJECT: Project = {
 };
 
 const ARCHIVED_PROJECT: Project = {
-  archivedAt: "2024-01-02T00:00:00.000Z",
   createdAt: "2024-01-01T00:00:00.000Z",
   description: "归档描述",
   id: "p2",
@@ -57,7 +55,6 @@ function createProjectFetchMock(initialProjects: Project[] = [ACTIVE_PROJECT, AR
     if (url.pathname === "/api/projects" && call.method === "POST") {
       const data = jsonBody(call.body) as { description?: string; name: string };
       const created: Project = {
-        archivedAt: null,
         createdAt: "2024-01-03T00:00:00.000Z",
         description: data.description ?? "",
         id: "p-created",
@@ -83,13 +80,13 @@ function createProjectFetchMock(initialProjects: Project[] = [ACTIVE_PROJECT, AR
       }
 
       if (call.method === "POST" && action === "archive") {
-        const archived = { ...project, archivedAt: "2024-01-04T00:00:00.000Z", status: "archived" as const };
+        const archived = { ...project, status: "archived" as const };
         projects = projects.map((item) => (item.id === id ? archived : item));
         return jsonResponse({ project: archived });
       }
 
       if (call.method === "POST" && action === "restore") {
-        const restored = { ...project, archivedAt: null, status: "active" as const };
+        const restored = { ...project, status: "active" as const };
         projects = projects.map((item) => (item.id === id ? restored : item));
         return jsonResponse({ project: restored });
       }