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/991_w6a_ww.c

@@ -1,15 +1,9 @@
 /*
- * 991_w6a_ww — explicit bootstrap gate for the ww-side w6a port.
- *
- * Diffs the C-built `w6a` against the ww-built `w6a_ww` on a corpus of
- * .s files. Both must produce byte-identical ELF .o output. The corpus
- * spans:
- *   - rt/X.s              hand-written runtime; small, varied operands
- *   - generated .s        from the existing selfhost cgen pipeline
- *                         (wwdump/w6a/w6l main.s) - large, exercises
- *                         every encoding path w6c emits
- *
- * Any divergence is a port bug in selfhost/cmd/w6a/.
+ * Explicit bootstrap gate: the C-built `w6a` and the ww-built `w6a_ww`
+ * must produce byte-identical ELF .o output over the corpus. Any
+ * divergence is a port bug in selfhost/cmd/w6a/. The corpus pairs
+ * hand-written rt/X.s (small, varied operands) with cgen-generated .s
+ * (large — exercises every encoding path w6c emits).
  */
 #include <stdio.h>
 #include <stdlib.h>