feat: implement user profile management and oauth/traefik integration

User Profile (US-004):
- Add authenticated profile endpoints (GET/PUT /users/me)
- Add avatar upload with file validation (PNG/JPEG, max 2MB)
- Create frontend profile page with edit form and avatar upload
- Update app shell to link to profile page

OAuth/Traefik Integration:
- Externalize all Authentik URLs to environment variables
- Add domain configuration (API_DOMAIN, WEB_DOMAIN, AUTHENTIK_DOMAIN)
- Create docker-compose.traefik.yml for reverse proxy deployment
- Update OAuth redirect/callback URLs to use configured domains
- Add VITE_APP_URL for frontend public URL configuration

Quality gates: pytest (50 passed), ruff, mypy, npm test (12 passed), typecheck, lint, build

apps/web/src/components/app-shell.tsx

@@ -20,7 +20,9 @@ export const AppShell = () => {
           Headquarter
         </Link>
         <div className="header-actions">
-          <div className="user-chip">{user?.name ?? "User"}</div>
+          <Link className="user-chip" to="/profile">
+            {user?.name ?? "User"}
+          </Link>
           <button
             className="ghost-button"
             onClick={() => {