[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/Migrations/AppDbContextModelSnapshot.cs

@@ -66,6 +66,9 @@ namespace JobsMedical.Web.Migrations
                     b.Property<bool>("BaleEnabled")
                         .HasColumnType("boolean");
 
+                    b.Property<bool>("DemoMode")
+                        .HasColumnType("boolean");
+
                     b.Property<string>("DivarCity")
                         .HasMaxLength(60)
                         .HasColumnType("character varying(60)");
@@ -133,6 +136,13 @@ namespace JobsMedical.Web.Migrations
                         .HasMaxLength(120)
                         .HasColumnType("character varying(120)");
 
+                    b.Property<string>("WebsiteUrls")
+                        .HasMaxLength(4000)
+                        .HasColumnType("character varying(4000)");
+
+                    b.Property<bool>("WebsitesEnabled")
+                        .HasColumnType("boolean");
+
                     b.HasKey("Id");
 
                     b.ToTable("AppSettings");
@@ -297,6 +307,9 @@ namespace JobsMedical.Web.Migrations
                     b.Property<int?>("DistrictId")
                         .HasColumnType("integer");
 
+                    b.Property<bool>("IsDemo")
+                        .HasColumnType("boolean");
+
                     b.Property<bool>("IsVerified")
                         .HasColumnType("boolean");