[Demo] Add admin demo-mode toggle + generic website ingest source

- AppSetting: DemoMode, WebsitesEnabled, WebsiteUrls
- Facility.IsDemo flag; SeedData split into SeedReferenceAsync (always)
  + SeedDemoAsync/ClearDemoAsync (idempotent, toggleable at runtime)
- WebsiteListingSource: scrape any admin-configured URL (og:title + content)
- Admin Settings: seed/clear demo card, demo-mode checkbox, website source
  fields; Program.cs seeds demo when DemoMode on (or in Development)
- EF migration DemoModeAndWebsites

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

src/JobsMedical.Web/Services/Scraping/SettingsService.cs

@@ -41,6 +41,9 @@ public class SettingsService
         s.TelegramChannels = incoming.TelegramChannels?.Trim();
         s.BaleEnabled = incoming.BaleEnabled;
         s.BaleBotToken = incoming.BaleBotToken?.Trim();
+        s.DemoMode = incoming.DemoMode;
+        s.WebsitesEnabled = incoming.WebsitesEnabled;
+        s.WebsiteUrls = incoming.WebsiteUrls?.Trim();
         s.DivarEnabled = incoming.DivarEnabled;
         s.DivarCity = string.IsNullOrWhiteSpace(incoming.DivarCity) ? "tehran" : incoming.DivarCity.Trim();
         s.DivarQueries = incoming.DivarQueries?.Trim();