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

package-lock.json

@@ -17,6 +17,7 @@
         "@nestjs/platform-express": "^11.1.18",
         "@nestjs/swagger": "^11.2.6",
         "@nestjs/typeorm": "^11.0.1",
+        "acorn": "^8.16.0",
         "better-sqlite3": "^12.8.0",
         "class-transformer": "^0.5.1",
         "class-validator": "^0.14.4",
@@ -30,6 +31,7 @@
       },
       "devDependencies": {
         "@nestjs/cli": "^11.0.17",
+        "@types/acorn": "^4.0.6",
         "@types/better-sqlite3": "^7.6.13",
         "@types/jsdom": "^28.0.1",
         "@types/mozilla__readability": "^0.4.2",
@@ -1377,6 +1379,16 @@
       "integrity": "sha512-OvjF+z51L3ov0OyAU0duzsYuvO01PH7x4t6DJx+guahgTnBHkhJdG7soQeTSFLWN3efnHyibZ4Z8l2EuWwJN3A==",
       "license": "MIT"
     },
+    "node_modules/@types/acorn": {
+      "version": "4.0.6",
+      "resolved": "https://registry.npmjs.org/@types/acorn/-/acorn-4.0.6.tgz",
+      "integrity": "sha512-veQTnWP+1D/xbxVrPC3zHnCZRjSrKfhbMUlEA43iMZLu7EsnTtkJklIuwrCPbOi8YkvDQAiW05VQQFvvz9oieQ==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@types/estree": "*"
+      }
+    },
     "node_modules/@types/better-sqlite3": {
       "version": "7.6.13",
       "resolved": "https://registry.npmjs.org/@types/better-sqlite3/-/better-sqlite3-7.6.13.tgz",
@@ -1678,7 +1690,6 @@
       "version": "8.16.0",
       "resolved": "https://registry.npmjs.org/acorn/-/acorn-8.16.0.tgz",
       "integrity": "sha512-UVJyE9MttOsBQIDKw1skb9nAwQuR5wuGD3+82K6JgJlm/Y+KI92oNsMNGZCYdDsVtRHSak0pcV5Dno5+4jh9sw==",
-      "dev": true,
       "license": "MIT",
       "bin": {
         "acorn": "bin/acorn"