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/lang/alias_structlit_init_test.ww

@@ -1,4 +1,4 @@
-// alias_structlit_init_test — #63: let-init from an alias-NAMED struct
+// #63: let-init from an alias-NAMED struct
 // LITERAL, migrated from test/wcc/944_alias_structlit_init_run.c (#5-C3).
 // wwstage's cglet N_STRUCTLIT arm resolved the struct by a BARE
 // structlookup(sname): for an alias `type rep2 = rep` only the base `rep` is