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/Services/Scraping/SettingsService.cs

@@ -46,6 +46,10 @@ public class SettingsService
         s.DivarQueries = incoming.DivarQueries?.Trim();
         s.MedjobsEnabled = incoming.MedjobsEnabled;
         s.MedjobsMaxAds = Math.Clamp(incoming.MedjobsMaxAds, 1, 500);
+        s.SmsEnabled = incoming.SmsEnabled;
+        s.SmsApiKey = incoming.SmsApiKey?.Trim();
+        s.SmsTemplate = incoming.SmsTemplate?.Trim();
+        s.SmsSender = incoming.SmsSender?.Trim();
         s.UpdatedAt = DateTime.UtcNow;
         await _db.SaveChangesAsync();
     }