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/profile/+page.server.ts

@@ -0,0 +1,54 @@
+import { fail } from '@sveltejs/kit';
+import type { PageServerLoad, Actions } from './$types';
+import { createApiClient } from '$lib/api.server';
+import { getErrorMessage } from '$lib/errors';
+
+export const load: PageServerLoad = async ({ locals }) => {
+	return { user: locals.user };
+};
+
+export const actions: Actions = {
+	updateProfile: async ({ request, fetch }) => {
+		const formData = await request.formData();
+		const body = {
+			firstName: formData.get('firstName')?.toString().trim() || undefined,
+			lastName: formData.get('lastName')?.toString().trim() || undefined,
+			birthDate: (formData.get('birthDate')?.toString() || undefined) as string | undefined,
+			email: formData.get('email')?.toString().trim() || undefined,
+			contact: formData.get('contact')?.toString().trim() || undefined
+		};
+
+		const api = createApiClient(fetch);
+		const result = await api.PUT('/api/users/me', { body });
+
+		if (!result.response.ok) {
+			const code = (result.error as unknown as { code?: string })?.code;
+			return fail(result.response.status, { updateError: getErrorMessage(code) });
+		}
+
+		return { updateSuccess: true };
+	},
+
+	changePassword: async ({ request, fetch }) => {
+		const formData = await request.formData();
+		const currentPassword = formData.get('currentPassword')?.toString() ?? '';
+		const newPassword = formData.get('newPassword')?.toString() ?? '';
+		const confirmPassword = formData.get('confirmPassword')?.toString() ?? '';
+
+		if (newPassword !== confirmPassword) {
+			return fail(400, { passwordError: 'PASSWORDS_DO_NOT_MATCH' });
+		}
+
+		const api = createApiClient(fetch);
+		const result = await api.POST('/api/users/me/password', {
+			body: { currentPassword, newPassword }
+		});
+
+		if (!result.response.ok) {
+			const code = (result.error as unknown as { code?: string })?.code;
+			return fail(result.response.status, { passwordError: getErrorMessage(code) });
+		}
+
+		return { passwordSuccess: true };
+	}
+};