feat: 添加完整的单元测试套件

- 新增 vitest 测试框架配置
- 添加 54 个测试文件，共 951 个测试用例
- 覆盖核心模块：
  - Agent: executor, registry, config-loader, permission-merger
  - Context: manager, compaction, prune, token-counter
  - Permission: manager, bash/file/git/web checkers, wildcard
  - Session: manager, storage
  - Tools: filesystem (12个), git (10个), web, shell, todo, task
  - LSP: client, server, language
  - Utils: config, diff
  - UI: terminal

vitest.config.ts

@@ -0,0 +1,27 @@
+import { defineConfig } from 'vitest/config';
+
+export default defineConfig({
+  test: {
+    globals: true,
+    environment: 'node',
+    include: ['tests/**/*.test.ts'],
+    exclude: ['node_modules', 'dist'],
+    coverage: {
+      provider: 'v8',
+      reporter: ['text', 'json', 'html'],
+      include: ['src/**/*.ts'],
+      exclude: [
+        'src/index.ts',
+        'src/ui/**',
+        'src/tools/descriptions/**',
+      ],
+    },
+    setupFiles: ['tests/setup.ts'],
+    testTimeout: 10000,
+  },
+  resolve: {
+    alias: {
+      '@': '/src',
+    },
+  },
+});