Add user account settings page with profile management

- Add /account route with profile form (firstName, lastName, address, IBAN)
- Create UserProfile type and MongoDB users collection
- Implement server actions for getting and updating user profile
- Add Account Circle icon to PageHeader linking to /account
- Install Material UI icons for account icon
- Add form input disabling during save with loading spinner
- Add cancel button to discard changes and return home
- Add English and Croatian translations for account page
- Update locale names with flag emojis in language selector

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/lib/actions/userProfileActions.ts

@@ -0,0 +1,100 @@
+'use server';
+
+import { z } from 'zod';
+import { getDbClient } from '../dbClient';
+import { UserProfile } from '../db-types';
+import { withUser } from '@/app/lib/auth';
+import { AuthenticatedUser } from '../types/next-auth';
+import { unstable_noStore as noStore } from 'next/cache';
+import { IntlTemplateFn } from '@/app/i18n';
+import { getTranslations } from "next-intl/server";
+import { revalidatePath } from 'next/cache';
+
+export type State = {
+    errors?: {
+        firstName?: string[];
+        lastName?: string[];
+        address?: string[];
+        iban?: string[];
+    };
+    message?: string | null;
+    success?: boolean;
+};
+
+/**
+ * Schema for validating user profile form fields
+ */
+const FormSchema = (t: IntlTemplateFn) => z.object({
+    firstName: z.string().optional(),
+    lastName: z.string().optional(),
+    address: z.string().optional(),
+    iban: z.string().optional(),
+});
+
+/**
+ * Get user profile
+ */
+export const getUserProfile = withUser(async (user: AuthenticatedUser) => {
+    noStore();
+
+    const dbClient = await getDbClient();
+    const { id: userId } = user;
+
+    const profile = await dbClient.collection<UserProfile>("users")
+        .findOne({ userId });
+
+    return profile;
+});
+
+/**
+ * Update user profile
+ */
+export const updateUserProfile = withUser(async (user: AuthenticatedUser, prevState: State, formData: FormData) => {
+    noStore();
+
+    const t = await getTranslations("account-form.validation");
+
+    const validatedFields = FormSchema(t).safeParse({
+        firstName: formData.get('firstName') || undefined,
+        lastName: formData.get('lastName') || undefined,
+        address: formData.get('address') || undefined,
+        iban: formData.get('iban') || undefined,
+    });
+
+    // If form validation fails, return errors early. Otherwise, continue...
+    if (!validatedFields.success) {
+        return {
+            errors: validatedFields.error.flatten().fieldErrors,
+            message: "Validation failed",
+            success: false,
+        };
+    }
+
+    const { firstName, lastName, address, iban } = validatedFields.data;
+
+    // Update the user profile in MongoDB
+    const dbClient = await getDbClient();
+    const { id: userId } = user;
+
+    const userProfile: UserProfile = {
+        userId,
+        firstName: firstName || null,
+        lastName: lastName || null,
+        address: address || null,
+        iban: iban || null,
+    };
+
+    await dbClient.collection<UserProfile>("users")
+        .updateOne(
+            { userId },
+            { $set: userProfile },
+            { upsert: true }
+        );
+
+    revalidatePath('/account');
+
+    return {
+        message: null,
+        success: true,
+    };
+});