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/arr_struct_subtail_frame_test.ww

@@ -1,4 +1,4 @@
-// arr_struct_subtail_frame_test — #9: a local `[N]S` where S is a struct with
+// #9: a local `[N]S` where S is a struct with
 // a sub-8-tail field over-sized its stack FRAME (cs≠ww, gate-visible). The
 // wwstage cgen frame reader (slotsize, cgenutil.ww TY_ARRAY arm) summed the
 // element's slot-PADDED width (outer.slotsize 24) × N instead of the array's
@@ -43,7 +43,7 @@ type outer = struct { a: u8, p: inner, z: i64 }; // natural 16, align 8 (sub-8 t
 	assert(arr[1].z == 200i64);
 };
 
-@test fn write_tail() void = {                 // write the sub-8 tail field then read back
+@test fn write_tail() void = {
 	let arr: [2]outer = [
 		outer { a = 1u8, p = inner { x = 2u8, y = 3u8 }, z = 100i64 },
 		outer { a = 4u8, p = inner { x = 5u8, y = 6u8 }, z = 200i64 }];