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/routes/users/[id]/+page.server.ts

@@ -0,0 +1,16 @@
+import { error } from '@sveltejs/kit';
+import type { PageServerLoad } from './$types';
+import { createApiClient } from '$lib/api.server';
+import { getErrorMessage } from '$lib/errors';
+
+export const load: PageServerLoad = async ({ params, fetch }) => {
+	const api = createApiClient(fetch);
+	const result = await api.GET('/api/users/{id}', { params: { path: { id: params.id } } });
+
+	if (!result.response.ok) {
+		const code = (result.error as unknown as { code?: string })?.code;
+		throw error(result.response.status, getErrorMessage(code));
+	}
+
+	return { profileUser: result.data! };
+};