Replace contact form POST with async JS API endpoint

Add a POST /api/contact minimal API that returns JSON instead of relying
on the Razor Page's OnPostAsync full-page reload. The contact form now
submits via fetch(), showing an inline success or error message without
reloading the page.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SLdp8vEGVX6EKSDQPAx36a

RazorPagesMovie/Pages/Bewerbung.cshtml.cs

@@ -1,62 +1,12 @@
-using Microsoft.AspNetCore.Mvc;
 using Microsoft.AspNetCore.Mvc.RazorPages;
-using RazorPagesMovie.Data;
-using RazorPagesMovie.Models;
 
 namespace RazorPagesMovie.Pages
 {
     public class BewerbungModel : PageModel
     {
-        private readonly RazorPagesMovieContext _context;
-
-        public BewerbungModel(RazorPagesMovieContext context)
-        {
-            _context = context;
-        }
-
-        [BindProperty]
-        public string Name { get; set; } = string.Empty;
-
-        [BindProperty]
-        public string Email { get; set; } = string.Empty;
-
-        [BindProperty]
-        public string? Phone { get; set; }
-
-        [BindProperty]
-        public string? Subject { get; set; }
-
-        [BindProperty]
-        public string Message { get; set; } = string.Empty;
-
-        public bool ContactFormSubmitted { get; set; }
-
         public void OnGet()
         {
 
         }
-
-        public async Task<IActionResult> OnPostAsync()
-        {
-            var contactMessage = new ContactMessage
-            {
-                Name = Name,
-                Email = Email,
-                Phone = Phone,
-                Subject = Subject,
-                Message = Message
-            };
-
-            if (!TryValidateModel(contactMessage, nameof(ContactMessage)))
-            {
-                return Page();
-            }
-
-            _context.ContactMessage.Add(contactMessage);
-            await _context.SaveChangesAsync();
-
-            ContactFormSubmitted = true;
-            return Page();
-        }
     }
 }