feat(frontend): add profile page and public user profile page

/profile: two-card layout with personal info form (name, birth date,
email, contact) and password change form, each with independent actions.
/users/[id]: read-only public view showing name, username, email, contact
with avatar circle initials.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/app.d.ts

@@ -6,10 +6,17 @@ declare global {
 		interface User {
 			id: string;
 			username: string;
+			firstName?: string;
+			lastName?: string;
+			birthDate?: string;
+			email?: string;
+			contact?: string;
 			groups: {
 				name: string;
 				permissions: string[];
 			}[];
+			enabled: boolean;
+			createdAt: string;
 		}
 
 		interface Locals {