Add SEO sitemap/robots + real SMS OTP (Kavenegar, admin-configured)

- /sitemap.xml (static pages + open shifts + fresh jobs, respecting expiry) + /robots.txt (blocks /Admin,/Employer); base URL from forwarded request → https://hamkadr.ir in prod
- ISmsSender + KavenegarSmsSender (verify/lookup template, sms/send fallback); SMS settings (enabled/apikey/template/sender) in /Admin/Settings; OtpService.IssueAsync sends SMS and stops revealing the code when enabled (dev still shows it); migration

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

src/JobsMedical.Web/Pages/Account/Login.cshtml

@@ -44,9 +44,13 @@
             {
                 <div class="alert alert-success">
                     کد تأیید (حالت توسعه): <strong dir="ltr">@Model.DevCode</strong><br />
-                    <span style="font-size:12px;">در نسخه‌ی نهایی این کد از طریق پیامک (کاوه‌نگار/SMS.ir) ارسال می‌شود.</span>
+                    <span style="font-size:12px;">در حالت عادی این کد با پیامک ارسال می‌شود.</span>
                 </div>
             }
+            else
+            {
+                <div class="alert alert-success">کد تأیید با پیامک به شماره شما ارسال شد.</div>
+            }
             <form method="post">
                 <input type="hidden" name="Phone" value="@Model.Phone" />
                 <input type="hidden" name="AccountType" value="@Model.AccountType" />

src/JobsMedical.Web/Pages/Account/Login.cshtml.cs

@@ -36,7 +36,7 @@ public class LoginModel : PageModel
 
     public void OnGet() { }
 
-    public IActionResult OnPostRequestCode()
+    public async Task<IActionResult> OnPostRequestCodeAsync()
     {
         var phone = OtpService.Normalize(Phone);
         if (phone.Length < 10)
@@ -45,7 +45,7 @@ public class LoginModel : PageModel
             return Page();
         }
         Phone = phone;
-        DevCode = _otp.Issue(phone);   // dev: surface the code; prod: SMS gateway sends it
+        DevCode = await _otp.IssueAsync(phone);   // null when SMS is enabled (sent via gateway)
         CodeSent = true;
         return Page();
     }