Fix: blank profile page - implement UserProfile component and REST endpoint

[ImranFarhat01]

Problem

• /dashboard/profile route existed in the router but had no component assigned — the page was completely blank
• last_login was never updated on login because the custom token auth view did not call Django's login(), so it always showed null

Fix

• Created UserProfile React component with avatar, schematic/simulation stats, view mode, edit mode, and change password dialog
• Added UserProfileSerializer exposing id, username, email, first_name, last_name, date_joined, last_login
• Added UserProfileUpdateSerializer for PATCH requests (editable fields only)
• Added UserProfileView REST endpoint at /api/auth/user/profile/
• Wired /dashboard/profile route to UserProfile component
• Added autoComplete="new-password" to password fields to prevent browser autofill
• Merged PATCH response into existing profile state to preserve read-only fields like date_joined after editing
• Updated last_login on token auth to reflect actual login time

Testing

• Profile page loads with correct user data (username, email, member since, last login, schematic count)
• Edit profile updates fields and shows success toast; date_joined is preserved after save
• Change password dialog opens with empty fields (no autofill)
• Last login updates correctly after each login