Remove UseHeadlessBrowser from JobProvider — all fetches now go via page-fetcher-api

page-fetcher-api always uses Playwright (networkidle by default), so the
per-provider flag that chose between headless and plain HTTP is obsolete.

- Removed from JobProviderEntity, CvSearchDbContext, JobProviderConfig, JobTokenService
- HtmlJobSearcher no longer passes WaitFor (uses page-fetcher-api default)
- EF migration drops the column from cvSearch.JobProviders

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Apis/cv-search-data/Migrations/CvSearchDbContextModelSnapshot.cs

@@ -69,11 +69,6 @@ namespace CvSearch.Data.Migrations
                         .HasMaxLength(1024)
                         .HasColumnType("nvarchar(1024)");
 
-                    b.Property<bool>("UseHeadlessBrowser")
-                        .ValueGeneratedOnAdd()
-                        .HasColumnType("bit")
-                        .HasDefaultValue(false);
-
                     b.HasKey("Id");
 
                     b.ToTable("JobProviders", "cvSearch");