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/wwtestpkg.h

@@ -1,5 +1,5 @@
 /*
- * wwtestpkg.h — strict-package (#24a) test support.
+ * Strict-package (#24a) test support.
  *
  * Inline ww test fixtures historically omitted the `package main;` clause
  * that the parser now requires (a missing clause is a hard error). These