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/xmod/label_test.ww

@@ -71,8 +71,6 @@ fn catasm(sepdir: str) str = {
 	return out;
 };
 
-// ---- fnlabel (#9 + #12) ------------------------------------------------
-
 @test fn fnlabel() void = {
 	let fixdir: str = strings.concat(testenv.repo(),
 		"/test/wcc/data/fnlabelmangle");
@@ -107,8 +105,6 @@ fn catasm(sepdir: str) str = {
 	testenv.clean(td);
 };
 
-// ---- mklabel (#13) -----------------------------------------------------
-
 fn mod1locate() str = {
 	return strings.concat(
 		"package mod1;\n",