fix: production readiness — resolve build, lint, and code quality issues

- Fix Next.js build failure: remove duplicate route at (dashboard)/listings/[id]
  that conflicted with (public)/listings/[id] (same URL path in two route groups)
- Fix 772 ESLint errors: auto-fix import ordering (import-x/order), remove unused
  imports/variables, convert empty interfaces to type aliases, replace require()
  with ESM imports, fix consistent-type-imports violations
- Add CLAUDE.md for developer onboarding documentation
- All checks pass: 0 lint errors, typecheck clean, 230 tests passing, build success

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/api/src/modules/notifications/infrastructure/services/fcm.service.ts

@@ -1,6 +1,12 @@
 import { Injectable, type OnModuleInit } from '@nestjs/common';
-import { LoggerService } from '@modules/shared/infrastructure/logger.service';
-import * as admin from 'firebase-admin';
+import {
+  apps,
+  initializeApp,
+  credential,
+  messaging,
+  type ServiceAccount,
+} from 'firebase-admin';
+import { type LoggerService } from '@modules/shared/infrastructure/logger.service';
 
 export interface SendPushDto {
   token: string;
@@ -26,9 +32,9 @@ export class FcmService implements OnModuleInit {
     }
 
     try {
-      const serviceAccount = JSON.parse(serviceAccountJson) as admin.ServiceAccount;
-      if (!admin.apps.length) {
-        admin.initializeApp({ credential: admin.credential.cert(serviceAccount) });
+      const serviceAccount = JSON.parse(serviceAccountJson) as ServiceAccount;
+      if (!apps.length) {
+        initializeApp({ credential: credential.cert(serviceAccount) });
       }
       this.initialized = true;
       this.logger.log('Firebase Admin initialized for push notifications', 'FcmService');
@@ -50,7 +56,7 @@ export class FcmService implements OnModuleInit {
     }
 
     try {
-      const messageId = await admin.messaging().send({
+      const messageId = await messaging().send({
         token: dto.token,
         notification: {
           title: dto.title,