test: banner purge + WHY-only comment sweep (rule 8)

Every section banner dies (103 -> 0) across test/lang, the observer
suites, the C carriers, and the five comment-heavy corpus fixtures;
banner provenance (#N cites, carrier numbers, repair-cluster labels)
folded into headers or adjacent WHY comments. Narration deleted; row
provenance, ref cites, divergence pins, and layout contracts kept
(fwd-ref decl-order guards and bootstrap-gate corpus rationale
restored where the sweep over-cut). Comment-only proven: all 3742
wwbuild workdir .s byte-identical before/after; test-commit and
test-byteid (161 lang + 1399 data, 0 pinned-divergent) green.

test/wcc/000_smoke.c

@@ -1,9 +1,4 @@
-/*
- * 000_smoke — Phase 0 smoke test.
- *
- * Asserts arena allocation and growth through libwcc, plus the configured
- * version constant.  Driver behavior belongs to the driver integration tests.
- */
+/* Driver behavior belongs to the driver integration tests. */
 #include "ww.h"
 #include <stdlib.h>
 #include <string.h>