Replace hardcoded `localhost:8080` URLs with a centralised Axios instance

[Thunder-Blaze]

NotesPage.jsx and login.jsx both hardcode http://localhost:8080 in every Axios call. This makes it impossible to change the backend URL without editing multiple files.
Create a centralised frontend/src/api.js that exports a configured Axios instance using VITE_API_BASE_URL from .env.
Replace all raw axios.get/post/put/delete calls in NotesPage.jsx and login.jsx with the new instance.

• Touches: frontend/src/NotesPage.jsx, frontend/src/login.jsx, new frontend/src/api.js, frontend/.env

[sudhanshujvd]

/assign

[mini-walkerx]

@sudhanshujvd You are already assigned to 2 active issues across repositories. Please finish those before taking on more.

[mini-walkerx]

@sudhanshujvd You are already assigned to 2 active issues across repositories. Please finish those before taking on more.

[RGB-Tabla]

/assign

[mini-walkerx]

✅ Successfully assigned to @RGB-Tabla.

You have 5 hours to complete this issue (Deadline: Sun, 12 Apr 2026 04:25:40 GMT).

[mini-walkerx]

⏰ @RGB-Tabla's time to complete this issue has expired. They have been unassigned. Waitlist logic will pick up the next user...