Alpha: Frontend — App scaffold (React + Router) and Auth (Signup/Signin/Me)

[coderabbitai]

Context / backlinks:

• Requested by @shiv7shukla on March 17, 2026
• PR added signupcontroller #1: added signupcontroller #1

Goal:
Create the initial frontend structure and basic auth screens.

Scope:

• Set up React Router with public (signin/signup) and private (app) routes
• Build minimal Signup and Signin forms
• On success, store basic user state and navigate to the app shell
• Call /auth/me on load to refresh session

Acceptance criteria:

• Users can sign up and sign in from the UI
• Auth state persists via cookie-backed session (no tokens in localStorage)
• /auth/me auto-runs on app load to populate user or redirect to signin
• Basic error display for invalid credentials