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/hooks/use-models.test.ts

@@ -14,9 +14,9 @@ const MODEL = {
   capabilities: ["text"] as Array<"text">,
   contextLength: null,
   createdAt: "2024-01-01T00:00:00.000Z",
+  externalId: "gpt-4o",
   id: "m1",
   maxOutputTokens: null,
-  modelId: "gpt-4o",
   name: "GPT-4o",
   providerId: "pv1",
   updatedAt: "2024-01-01T00:00:00.000Z",
@@ -59,7 +59,7 @@ describe("use-models request helpers", () => {
 
     await createModel({
       capabilities: ["text"],
-      modelId: "gpt-4o",
+      externalId: "gpt-4o",
       name: "GPT-4o",
       providerId: "pv1",
     });
@@ -75,7 +75,7 @@ describe("use-models request helpers", () => {
     ]);
     expect(jsonBody(calls[0]?.body)).toEqual({
       capabilities: ["text"],
-      modelId: "gpt-4o",
+      externalId: "gpt-4o",
       name: "GPT-4o",
       providerId: "pv1",
     });
@@ -86,7 +86,7 @@ describe("use-models request helpers", () => {
     installFetchMock(() => jsonResponse({ error: "模型名称已存在" }, { status: 409 }));
 
     await expectRejectsWithMessage(
-      () => createModel({ capabilities: ["text"], modelId: "gpt-4o", name: "重复", providerId: "pv1" }),
+      () => createModel({ capabilities: ["text"], externalId: "gpt-4o", name: "重复", providerId: "pv1" }),
       "模型名称已存在",
     );
   });
@@ -100,12 +100,12 @@ describe("use-models request helpers", () => {
   test("testModelConnection 调用正确 URL 和 body", async () => {
     const calls = installFetchMock(() => jsonResponse({ modelTestResponse: { message: "模型连接成功", ok: true } }));
 
-    const result = await testModelConnection({ modelId: "gpt-4o", providerId: "pv1" });
+    const result = await testModelConnection({ externalId: "gpt-4o", providerId: "pv1" });
 
     expect(result.ok).toBe(true);
     expect(result.message).toBe("模型连接成功");
     expect(calls[0]?.method).toBe("POST");
     expect(calls[0]?.url).toBe("/api/models/test");
-    expect(jsonBody(calls[0]?.body)).toEqual({ modelId: "gpt-4o", providerId: "pv1" });
+    expect(jsonBody(calls[0]?.body)).toEqual({ externalId: "gpt-4o", providerId: "pv1" });
   });
 });