fix(auth): allow develop OAuth env keys in generated runtime fallback

- add GitHub/Google develop OAuth keys to GENERATED_FALLBACK_KEYS
- unblock /api/auth/github and /api/auth/google on Netlify runtime where process.env may be empty
- keep fallback restricted to explicit allowlist keys

Author: LesiaUKR

frontend/lib/env/server-env.ts

@@ -35,6 +35,12 @@ const GENERATED_FALLBACK_KEYS = new Set([
   'DATABASE_URL_LOCAL',
   'AUTH_SECRET',
   'CSRF_SECRET',
+  'GOOGLE_CLIENT_ID_DEVELOP',
+  'GOOGLE_CLIENT_SECRET_DEVELOP',
+  'GOOGLE_CLIENT_REDIRECT_URI_DEVELOP',
+  'GITHUB_CLIENT_ID_DEVELOP',
+  'GITHUB_CLIENT_SECRET_DEVELOP',
+  'GITHUB_CLIENT_REDIRECT_URI_DEVELOP',
 ]);