Link pageFetcher.PageFetches to cvSearch.JobSearchSessions

Adds nullable JobSearchSessionId to PageFetchEntity and FetchPageRequest.
cv-search-job passes session.Id on every fetch so all Playwright page
loads for a job search session can be traced back to their session.
Includes index on JobSearchSessionId for efficient lookup.

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

Apis/page-fetcher-data/Migrations/PageFetchDbContextModelSnapshot.cs

@@ -53,6 +53,10 @@ namespace PageFetcher.Data.Migrations
                     b.Property<int?>("HttpStatusCode")
                         .HasColumnType("int");
 
+                    b.Property<string>("JobSearchSessionId")
+                        .HasMaxLength(64)
+                        .HasColumnType("nvarchar(64)");
+
                     b.Property<bool>("Success")
                         .HasColumnType("bit");
 
@@ -69,6 +73,8 @@ namespace PageFetcher.Data.Migrations
 
                     b.HasIndex("CreatedAt");
 
+                    b.HasIndex("JobSearchSessionId");
+
                     b.HasIndex("Url");
 
                     b.ToTable("PageFetches", "pageFetcher");