refactor: complete P0-P1 improvements

Constants migration:
- server-agent.ts: SERVER_CONSULTATION_STATUS, LANGUAGE_CODE
- troubleshoot-agent.ts: TROUBLESHOOT_STATUS
- notification.ts: NOTIFICATION_TYPE

API improvements:
- search-tool.ts: Zod schema validation for Brave/Context7 APIs
- api-helper.ts: Centralized API call utility with retry/timeout

Testing:
- kv-cache.test.ts: 38 test cases for cache abstraction

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/setup.ts

@@ -14,37 +14,47 @@ declare global {
   };
 }
 
-let db: D1Database;
+let db: D1Database | null = null;
 
 beforeAll(async () => {
-  // Miniflare 바인딩 가져오기
-  const bindings = getMiniflareBindings();
-  db = bindings.DB;
+  // Miniflare 바인딩 가져오기 (있을 경우만)
+  if (typeof getMiniflareBindings === 'function') {
+    try {
+      const bindings = getMiniflareBindings();
+      db = bindings.DB;
 
-  // 스키마 초기화
-  const schemaPath = join(__dirname, '../schema.sql');
-  const schema = readFileSync(schemaPath, 'utf-8');
+      // 스키마 초기화
+      const schemaPath = join(__dirname, '../schema.sql');
+      const schema = readFileSync(schemaPath, 'utf-8');
 
-  // 각 statement를 개별 실행
-  const statements = schema
-    .split(';')
-    .map(s => s.trim())
-    .filter(s => s.length > 0 && !s.startsWith('--'));
+      // 각 statement를 개별 실행
+      const statements = schema
+        .split(';')
+        .map(s => s.trim())
+        .filter(s => s.length > 0 && !s.startsWith('--'));
 
-  for (const statement of statements) {
-    await db.exec(statement);
+      for (const statement of statements) {
+        await db.exec(statement);
+      }
+    } catch (error) {
+      // Miniflare 바인딩이 없는 테스트는 skip
+      console.warn('Miniflare bindings not available, skipping DB setup');
+    }
   }
 });
 
 afterEach(async () => {
-  // 각 테스트 후 데이터 정리 (스키마는 유지)
-  await db.exec('DELETE FROM deposit_transactions');
-  await db.exec('DELETE FROM bank_notifications');
-  await db.exec('DELETE FROM user_deposits');
-  await db.exec('DELETE FROM user_domains');
-  await db.exec('DELETE FROM summaries');
-  await db.exec('DELETE FROM message_buffer');
-  await db.exec('DELETE FROM users');
+  // DB가 있을 경우만 정리
+  if (db) {
+    // 각 테스트 후 데이터 정리 (스키마는 유지)
+    await db.exec('DELETE FROM deposit_transactions');
+    await db.exec('DELETE FROM bank_notifications');
+    await db.exec('DELETE FROM user_deposits');
+    await db.exec('DELETE FROM user_domains');
+    await db.exec('DELETE FROM summaries');
+    await db.exec('DELETE FROM message_buffer');
+    await db.exec('DELETE FROM users');
+  }
 });
 
 /**