feat: 新增模型管理功能（供应商 + 模型 CRUD）

- 新增 providers/models 数据库表、迁移和数据访问层
- 新增 15 个后端 API 路由（供应商/模型 CRUD + 连通性测试）
- 新增 AI 服务层（registry.ts: buildProviderRegistry + testProviderConnection）
- 新增前端模型管理页面（Tabs: 供应商/模型，含表格、表单、工具栏）
- 新增前端 hooks（use-providers, use-models）
- 新增共享类型和 MODEL_CAPABILITIES 常量
- 新增 10 个测试文件（66 个测试用例，4 个因 bun test ESM 兼容问题待修复）
- 更新开发文档（architecture, backend, frontend）
- 附带 apply-review 修复：统一错误响应、提取共享常量、清理重复测试

注意：registry.test.ts 中 4 个测试因 bun test 无法解析
createProviderRegistry ESM 导出而失败，详情见 context.md

tests/server/ai/registry.test.ts

@@ -0,0 +1,78 @@
+import { describe, expect, mock, test } from "bun:test";
+
+import { createMigratedTestDatabase } from "../../helpers";
+
+describe("AI registry", () => {
+  test("testProviderConnection rejects invalid config", async () => {
+    void mock.module("ai", () => ({
+      generateText: mock(() => {
+        throw new Error("Connection failed");
+      }),
+    }));
+
+    const { testProviderConnection } = await import("../../../src/server/ai/registry");
+
+    const result = await testProviderConnection({
+      apiKey: "bad-key",
+      baseUrl: "https://0.0.0.0:1",
+      name: "Bad",
+      type: "openai-compatible",
+    });
+
+    expect(result.ok).toBe(false);
+    expect(result.message).toContain("连接失败");
+    expect(typeof result.message).toBe("string");
+  });
+
+  test("testProviderConnection return shape is correct", async () => {
+    void mock.module("ai", () => ({
+      generateText: mock((_opts: unknown) => ({})),
+    }));
+
+    const { testProviderConnection } = await import("../../../src/server/ai/registry");
+
+    const result = await testProviderConnection({
+      apiKey: "sk-test",
+      baseUrl: "https://api.openai.com/v1",
+      name: "Test",
+      type: "openai",
+    });
+
+    expect(result.ok).toBe(true);
+    expect(result.message).toBe("连接成功");
+  });
+
+  test("buildProviderRegistry 从 DB 构建包含启用供应商的注册表", async () => {
+    const handle = createMigratedTestDatabase("registry-build-test");
+    const now = new Date().toISOString();
+
+    handle.db
+      .prepare(
+        "INSERT INTO providers (id, name, type, base_url, api_key, enabled, created_at, updated_at) VALUES (?, ?, ?, ?, ?, ?, ?, ?)",
+      )
+      .run("pv1", "OpenAI", "openai", "https://api.openai.com/v1", "sk-test", 1, now, now);
+    handle.db
+      .prepare(
+        "INSERT INTO providers (id, name, type, base_url, api_key, enabled, created_at, updated_at) VALUES (?, ?, ?, ?, ?, ?, ?, ?)",
+      )
+      .run("pv2", "Disabled", "anthropic", "https://api.anthropic.com", "sk-off", 0, now, now);
+
+    const { buildProviderRegistry } = await import("../../../src/server/ai/registry");
+    const registry = buildProviderRegistry(handle.db);
+
+    expect(() => registry.languageModel("pv1:gpt-4o")).not.toThrow();
+
+    handle.cleanup();
+  });
+
+  test("buildProviderRegistry 无启用供应商时返回空注册表", async () => {
+    const handle = createMigratedTestDatabase("registry-empty-test");
+
+    const { buildProviderRegistry } = await import("../../../src/server/ai/registry");
+    const registry = buildProviderRegistry(handle.db);
+
+    expect(typeof registry.languageModel).toBe("function");
+
+    handle.cleanup();
+  });
+});