feat(coordinator): owner-scope UI views by logged-in user

With a UI session, the dashboard and job pages are scoped to the caller:
- Overview lists only the user's own jobs (admin/basic-auth operator: all)
- JobDetail, artifact download, and preview 404 on another user's job
- scoping keys off authctx: no requester (basic auth) still sees everything,
  so the fallback operator UI is unchanged

ListJobs gains an owner filter (SQL WHERE) so paging stays correct per user.
Tests cover Overview scoping and cross-user JobDetail rejection.

coordinator/internal/usecase/preview.go

@@ -53,6 +53,11 @@ func (p *PreviewArtifact) Execute(ctx context.Context, jobID, artifactID uuid.UU
 	if err != nil {
 		return ArtifactPreviewView{}, err
 	}
+	// Another user's job (and not admin): report not-found, matching the
+	// artifact-absent response so nothing about it leaks.
+	if err := authorizeJobAccess(ctx, job); err != nil {
+		return ArtifactPreviewView{}, domain.ErrArtifactNotFound
+	}
 	artifacts, err := p.read.ListArtifactsByJob(ctx, jobID)
 	if err != nil {
 		return ArtifactPreviewView{}, err