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-api-models/FetchPageRequest.cs

@@ -17,4 +17,10 @@ public sealed class FetchPageRequest
     /// Identifies the calling service for audit purposes (e.g. <c>cv-matcher-api</c>, <c>cv-search-job</c>).
     /// </summary>
     public string CallerService { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Optional reference to the job search session that triggered this fetch.
+    /// Stored on <c>pageFetcher.PageFetches</c> for cross-schema audit queries.
+    /// </summary>
+    public string? JobSearchSessionId { get; set; }
 }