refactor: 后端架构加固 — 泛型化、批量查询、bootstrap 统一、路径修复与 pageSize 上限

- CheckerDefinition 泛型化，HTTP/Command checker 移除 resolved target 断言
- 新增 ProbeStore.getAllRecentSamples 消除 targets 路由 N+1 查询
- 统一 getAllTargetStats 与 getTargetStats 的 availability 精度
- Engine rejected 结果写入 internal error 记录，提升可观测性
- 新增 bootstrap.ts 统一 dev/production 启动序列
- dataDir 相对路径改为基于配置文件目录解析
- validatePagination 增加 pageSize 上限 200 校验
- 修复 ErrorBoundary override 标记
- 更新 README/DEVELOPMENT 文档，新增完整测试覆盖

tests/server/checker/config-loader.test.ts

@@ -116,7 +116,7 @@ describe("loadConfig", () => {
     const config = await loadConfig(configPath);
     expect(config.host).toBe("127.0.0.1");
     expect(config.port).toBe(3000);
-    expect(config.dataDir).toBe("./data");
+    expect(config.dataDir).toBe(join(tempDir, "data"));
     expect(config.maxConcurrentChecks).toBe(20);
     expect(config.targets).toHaveLength(1);
     const t = config.targets[0]! as ResolvedHttpTarget;
@@ -205,7 +205,7 @@ targets:
     const config = await loadConfig(configPath);
     expect(config.host).toBe("0.0.0.0");
     expect(config.port).toBe(8080);
-    expect(config.dataDir).toBe("./my-data");
+    expect(config.dataDir).toBe(join(tempDir, "my-data"));
     expect(config.maxConcurrentChecks).toBe(5);
     expect(config.targets).toHaveLength(2);
 
@@ -228,6 +228,25 @@ targets:
     expect(cmd.command.maxOutputBytes).toBe(10485760);
   });
 
+  test("绝对 dataDir 保持不变", async () => {
+    const dataDir = join(tempDir, "absolute-data");
+    const configPath = join(tempDir, "absolute-data-dir.yaml");
+    await writeFile(
+      configPath,
+      `server:
+  dataDir: "${dataDir}"
+targets:
+  - name: "test"
+    type: http
+    http:
+      url: "http://example.com"
+`,
+    );
+
+    const config = await loadConfig(configPath);
+    expect(config.dataDir).toBe(dataDir);
+  });
+
   test("per-target 覆盖 defaults", async () => {
     const configPath = join(tempDir, "override.yaml");
     await writeFile(