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/web/app/(admin)/layout.tsx

@@ -1,8 +1,5 @@
 'use client';
 
-import Link from 'next/link';
-import { usePathname, useRouter } from 'next/navigation';
-import { useEffect } from 'react';
 import {
   LayoutDashboard,
   Users,
@@ -12,10 +9,12 @@ import {
   Menu,
   X,
 } from 'lucide-react';
-import { useState } from 'react';
-import { cn } from '@/lib/utils';
-import { useAuthStore } from '@/lib/auth-store';
+import Link from 'next/link';
+import { usePathname, useRouter } from 'next/navigation';
+import { useEffect, useState  } from 'react';
 import { Button } from '@/components/ui/button';
+import { useAuthStore } from '@/lib/auth-store';
+import { cn } from '@/lib/utils';
 
 const adminNavItems = [
   { href: '/admin', label: 'Dashboard', icon: LayoutDashboard },