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/misc/stampdiag_test.ww

@@ -45,7 +45,6 @@ fn selfcheck() void = {
 		"asserttyped"));
 };
 
-// w6c_ww -o /dev/null <src>: rc 0 and stderr free of asserttyped.
 fn stampprobe(label: str, srcpath: str) void = {
 	let td: str = testenv.fresh();
 	let av: []str = [testenv.driver("w6c_ww"), "-o", "/dev/null",