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>

e2e/api/listings-media.spec.ts

@@ -1,6 +1,4 @@
 import { test, expect, registerUser, createListing } from '../fixtures';
-import * as path from 'path';
-import * as fs from 'fs';
 
 test.describe('POST /listings/:id/media — Media upload', () => {
   let accessToken: string;

e2e/fixtures/auth.fixture.ts

@@ -58,7 +58,7 @@ export const test = base.extend<{
   testTokens: TokenPair;
   authedRequest: APIRequestContext;
 }>({
-  testUser: async ({}, use) => {
+  testUser: async (_fixtures, use) => {
     await use(createTestUser());
   },