feat(observability): add exception filter, logging interceptor, and CodeExecutorModule

- add HttpExceptionFilter logging BadRequestException at warn and InternalServerErrorException at error with cause chain
- add LoggingInterceptor logging request/response pairs at debug level with method, path, body, status, and duration
- extract CodeExecutorService into standalone CodeExecutorModule imported by BrowserModule and McpModule
- thread { cause: err } into all catch blocks across auth, browser, and code-executor services

src/mcp/mcp.module.ts

@@ -5,9 +5,10 @@ import { AuthModule } from '../auth/auth.module';
 import { SessionModule } from '../session/session.module';
 import { EnvironmentModule } from '../environment/environment.module';
 import { BrowserModule } from '../browser/browser.module';
+import { CodeExecutorModule } from '../code-executor/code-executor.module';
 
 @Module({
-  imports: [AuthModule, SessionModule, EnvironmentModule, BrowserModule],
+  imports: [AuthModule, SessionModule, EnvironmentModule, BrowserModule, CodeExecutorModule],
   controllers: [McpController],
   providers: [McpService],
 })