feat: integrate real backend API with centralized API client

- Add centralized apiPost() client (src/services/api.ts) that handles
  auth injection, error handling, and token expiry uniformly
- Implement real authentication against /accounts/api/login/ and /logout/
- Rewrite partnerApi and userAppApi to use centralized client
- Connect Partners page to /partner/list/ and /partner/create/ APIs
- Add Vite proxy rules for /accounts/api and /partner endpoints
- Update AuthUser type to match full backend user response
- Move NuqsAdapter inside BrowserRouter for correct routing context

Made-with: Cursor

.gitignore

@@ -11,6 +11,9 @@ node_modules
 dist
 dist-ssr
 *.local
+.env
+.env.*
+.npm-cache/
 
 # Editor directories and files
 .vscode/*