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

src/server/routes/models/create.ts

@@ -0,0 +1,47 @@
+import type Database from "bun:sqlite";
+
+import type { CreateModelRequest, RuntimeMode } from "../../../shared/api";
+
+import { MODEL_CAPABILITIES } from "../../../shared/api";
+import { createModel } from "../../db/models";
+import { createApiError, jsonResponse } from "../../helpers";
+
+export async function handleCreateModel(req: Request, db: Database, mode: RuntimeMode): Promise<Response> {
+  let body: CreateModelRequest;
+  try {
+    body = (await req.json()) as CreateModelRequest;
+  } catch {
+    return jsonResponse(createApiError("Invalid JSON body", 400), { mode, status: 400 });
+  }
+
+  if (!body.name || typeof body.name !== "string") {
+    return jsonResponse(createApiError("name is required", 400), { mode, status: 400 });
+  }
+
+  if (!body.modelId || typeof body.modelId !== "string") {
+    return jsonResponse(createApiError("modelId is required", 400), { mode, status: 400 });
+  }
+
+  if (!body.providerId || typeof body.providerId !== "string") {
+    return jsonResponse(createApiError("providerId is required", 400), { mode, status: 400 });
+  }
+
+  if (!Array.isArray(body.capabilities) || body.capabilities.length === 0) {
+    return jsonResponse(createApiError("capabilities is required and must be a non-empty array", 400), {
+      mode,
+      status: 400,
+    });
+  }
+
+  const invalidCaps = body.capabilities.filter((c) => !MODEL_CAPABILITIES.includes(c));
+  if (invalidCaps.length > 0) {
+    return jsonResponse(createApiError(`Invalid capabilities: ${invalidCaps.join(", ")}`, 400), { mode, status: 400 });
+  }
+
+  const result = createModel(db, body);
+  if ("error" in result) {
+    return jsonResponse(createApiError(result.error, result.status), { mode, status: result.status });
+  }
+
+  return jsonResponse(result, { mode, status: 201 });
+}