refactor: 统一 log.ts/debug.ts 的测试 mock 为共享定义

- 新增 tests/mocks/log.ts 和 tests/mocks/debug.ts，覆盖源文件全部实际导出
- 移除旧 mock 中不存在的导出（logToFile、logEvent、getLogFilePath）
- 13 个测试文件改为使用共享 mock，避免定义分散和不一致

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/services/langfuse/__tests__/langfuse.test.ts

@@ -1,4 +1,5 @@
 import { mock, describe, test, expect, beforeEach } from 'bun:test'
+import { debugMock } from '../../../../tests/mocks/debug'
 
 // Mock @langfuse/otel before any imports
 const mockForceFlush = mock(() => Promise.resolve())
@@ -71,9 +72,7 @@ mock.module('@langfuse/tracing', () => ({
 }))
 
 // Mock debug logger
-mock.module('src/utils/debug.ts', () => ({
-  logForDebugging: mock(() => {}),
-}))
+mock.module('src/utils/debug.ts', debugMock)
 
 // Mock user data — resolveLangfuseUserId uses getCoreUserData().email and .deviceId
 mock.module('src/utils/user.js', () => ({