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/byteid/wwi_test.ww

@@ -49,7 +49,6 @@ fn lifetime() time.duration = {
 	return (180i64 * (time.second: i64)): time.duration;
 };
 
-// Run argv in `dir`, true iff normal exit 0.
 fn runok(dir: str, name: str, argv: []str) bool = {
 	let co: testenv.commandout;
 	testenv.runcommand(dir, dir, name, argv, lifetime(), &co);
@@ -227,8 +226,6 @@ fn m2positive(pkg: str) void = {
 	testenv.clean(td);
 };
 
-// ---- wwileaf (#11) -----------------------------------------------------
-
 fn leafrow(tag: str, path: str, leaf: str, body: str, want: str) void = {
 	let td: str = testenv.fresh();
 	let prod: str = strings.concat(td, "/", tag, ".prod.ww");