feat: auth-flow

[FirezTheGreat]

Please describe the changes this PR makes and why it should be merged:

✅ Unified Auth Flow – Feature Checklist

🔐 Core Logic

• Create smart unified flow for /register and /login
• Add Zustand store useUIStore (loading, error, success)
• Connect error/success states to global toast handler (sonner)
• Add toast feedback via sonner throughout the flow
• Redirect known users from /register → /login with email autofill
• Redirect new users from /login → /register with email/password preserved

✉️ OTP Verification Flow

• Add OTP step to flow
• Implement OTP backend integration (/api/auth/start, /verify)
• Add expiration time for OTP (e.g. 5 minutes)
• Rate-limit OTP requests (e.g. 3 per 10 minutes per IP/email)
• Handle OTP errors (invalid, expired, rate-limited)

👤 Registration Details (New Users)

• Add password + name steps (multi-step flow)
• Create database schema for new users in MongoDB
• Prevent duplicate users after verification
• Hash password securely on backend
• Auto-login user and issue JWT after successful registration

🔐 Login Flow (Existing Users)

• Validate email/password via /api/auth/login
• On success, issue JWT and set secure cookie
• Redirect to dashboard after login
• Handle incorrect credentials via toast

🧠 UI & UX

• Form validation (email, password strength)
• Use useAppSeo to dynamically set title/description
• Smooth transitions between steps

✅ Completion Criteria

• Full happy-path and edge-case testing
• New user signup: email → OTP → name + password → onboarding
• Existing user login: email + password → dashboard
• Redirect handling between login/register
• JWT stored securely and user session initialized

Status and versioning classification:

• I know how to update typings and have done so, or typings don't need updating
• This PR changes the projects's interface (inbuilt methods or parameters added)
• This PR includes breaking changes (methods removed or renamed, parameters moved or removed)