bugfix: .env.example files updated. some minor changes in jwt strategy to avoid failing when .env files does not contain needed keys.

frontend/.env.example

@@ -0,0 +1,7 @@
+# Copy to .env.local for local development (Next.js loads .env.local automatically).
+# Do not commit .env.local — only this template is tracked in git.
+
+NEXT_PUBLIC_API_URL=http://localhost:3000/api
+NEXT_PUBLIC_APP_NAME=DyoLink
+# URL where users open the frontend (used for metadata, images, etc.)
+NEXT_PUBLIC_APP_URL=http://localhost:3001