chore(traces): put TRACES tags on their own line; regenerate the report

The parser reads a tag up to end of line, so `# TRACES: GR-004 | SR-001 —
prose` swallowed the prose into the tag and the row went unmatched. Splitting
the comment leaves the tag greppable by the same pattern as the code tags and
the commit trailers, which is the point of the house format.

Mechanical throughout; no logic touched. The regenerated report reflects this
session's new tags: 137 -> 148 found, and one more tagged-but-unexecuted, which
is the SuperHero accuracy assertion that is documented but not yet a test.

experiments/xsource/verify_labels.py

@@ -1,6 +1,14 @@
 #!/usr/bin/env python3
 """Integrity check on the labelled set, before it is used as ground truth.
 
+TRACES: VR-013 | PR-002
+
+VR-013's ground truth is hand-sorted rather than propagated by embedding
+similarity, because propagation would keep only the faces the embedder already
+gets right and silently drop the ones the sweep exists to find. This script is
+what makes that claim checkable, so it is part of the requirement rather than a
+helper of it.
+
 Checks, loudest failure first:
 
 1. INDEX INTEGRITY. Each crop's embedding is taken by re-detecting its source