perf(pipeline): parallel prefetch and lean revision GET

GetRevisionSummary без preview_fragments; boundedRepoCtx для GetRevision;
parallel CDN prefetch с ctx из ingest.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/httpapi/routes.go

@@ -579,7 +579,7 @@ func (s *Server) handleGetRevision(w http.ResponseWriter, r *http.Request) {
 	if !s.requireAtLeast(w, a, "viewer") {
 		return
 	}
-	rev, err := s.store.GetRevision(a.TenantID, r.PathValue("revision_id"))
+	rev, err := s.store.GetRevisionSummary(a.TenantID, r.PathValue("revision_id"))
 	if err != nil {
 		writeProblem(w, http.StatusNotFound, "Not Found", "revision not found")
 		return