Anti-abuse hardening: hourly posting rate limit + captcha on facility registration

- SubmissionGuard.PostingRateExceededAsync: max 20 new listings (shifts+jobs) per account per rolling hour, enforced in PostJob + PostShift
- Captcha + spam-name screen added to /Employer/RegisterFacility

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/JobsMedical.Web/Pages/Employer/RegisterFacility.cshtml.cs

@@ -15,10 +15,18 @@ namespace JobsMedical.Web.Pages.Employer;
 public class RegisterFacilityModel : PageModel
 {
     private readonly AppDbContext _db;
-    public RegisterFacilityModel(AppDbContext db) => _db = db;
+    private readonly CaptchaService _captcha;
+    public RegisterFacilityModel(AppDbContext db, CaptchaService captcha)
+    {
+        _db = db;
+        _captcha = captcha;
+    }
 
     public List<City> Cities { get; private set; } = new();
     public List<District> Districts { get; private set; } = new();
+    public string CaptchaQuestion { get; private set; } = "";
+    [BindProperty] public string? CaptchaToken { get; set; }
+    [BindProperty] public string? CaptchaAnswer { get; set; }
 
     [BindProperty] public string Name { get; set; } = "";
     [BindProperty] public FacilityType Type { get; set; }
@@ -31,16 +39,21 @@ public class RegisterFacilityModel : PageModel
     [BindProperty] public double? Lng { get; set; }
     public string? Error { get; private set; }
 
-    public async Task OnGetAsync() => await LoadListsAsync();
+    public async Task OnGetAsync() { await LoadListsAsync(); NewCaptcha(); }
 
     public async Task<IActionResult> OnPostAsync()
     {
         await LoadListsAsync();
+        if (!_captcha.Verify(CaptchaToken, CaptchaAnswer))
+        { Error = "پاسخ سؤال امنیتی نادرست است."; NewCaptcha(); return Page(); }
         if (string.IsNullOrWhiteSpace(Name) || CityId == 0)
         {
             Error = "نام مرکز و شهر الزامی است.";
+            NewCaptcha();
             return Page();
         }
+        if (SubmissionGuard.ContainsSpam(Name))
+        { Error = "نام مرکز نامعتبر به‌نظر می‌رسد."; NewCaptcha(); return Page(); }
 
         var userId = int.Parse(User.FindFirstValue(ClaimTypes.NameIdentifier)!);
         var facility = new Facility
@@ -81,4 +94,11 @@ public class RegisterFacilityModel : PageModel
         Cities = await _db.Cities.OrderByDescending(c => c.IsActive).ThenBy(c => c.Name).ToListAsync();
         Districts = await _db.Districts.Where(d => d.IsActive).OrderBy(d => d.Name).ToListAsync();
     }
+
+    private void NewCaptcha()
+    {
+        var (q, token) = _captcha.Create();
+        CaptchaQuestion = q;
+        CaptchaToken = token;
+    }
 }