Feature: Add password change functionality for admin and customers

- Add customer password change page at /account/change-password
- Add admin password change page at /admin/change-password
- Create AdminUser database table for storing admin credentials
- Admin login now checks database first, falls back to env vars
- Update admin auth to support bcrypt password hashing
- Add change password links to customer account and admin nav
- Fix customer login logs back link (was pointing to non-existent /admin)
- Add success/error message handling for password changes

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/app/account/page.tsx

@@ -25,10 +25,16 @@ function statusClasses(status: string, trackingNumber?: string | null) {
   return 'bg-splash-orange/10 text-splash-orange';
 }
 
-export default async function AccountPage() {
+const SUCCESS_MESSAGES: Record<string, string> = {
+  password_changed: 'Password updated successfully.',
+};
+
+export default async function AccountPage({ searchParams }: { searchParams: { success?: string } }) {
   const customer = await getCurrentCustomer();
   if (!customer) redirect('/account/login');
 
+  const success = searchParams.success ? SUCCESS_MESSAGES[searchParams.success] : null;
+
   const orders = await prisma.order.findMany({
     where: { customerId: customer.id },
     orderBy: { createdAt: 'desc' },
@@ -50,6 +56,11 @@ export default async function AccountPage() {
 
   return (
     <div className="mx-auto max-w-3xl px-6 py-12">
+      {success && (
+        <div className="mb-6 border border-green-500/40 bg-green-500/10 px-4 py-3 text-sm text-green-700">
+          ✓ {success}
+        </div>
+      )}
       <div className="flex items-baseline justify-between gap-3">
         <div>
           <h1 className="font-display text-3xl">My account</h1>
@@ -58,14 +69,22 @@ export default async function AccountPage() {
             {customer.email}
           </p>
         </div>
-        <form action={logoutCustomer}>
-          <button
-            type="submit"
+        <div className="flex gap-3">
+          <Link
+            href="/account/change-password"
             className="tag-label border border-line px-3 py-1.5 hover:border-clay hover:text-clay"
           >
-            Log out
-          </button>
-        </form>
+            Change password
+          </Link>
+          <form action={logoutCustomer}>
+            <button
+              type="submit"
+              className="tag-label border border-line px-3 py-1.5 hover:border-clay hover:text-clay"
+            >
+              Log out
+            </button>
+          </form>
+        </div>
       </div>
 
       <AddressFormSection customer={customer} />