toolchain: banner purge + WHY-only comment sweep (rule 8)

selfhost/, cmd/, internal/ join the tree-wide sweep: every section
banner dies (91 selfhost + the cmd C-style dividers -> 0); narration
and stale contracts deleted (pre-#22 bundler notes, retired
single-PT_LOAD and no-archive claims, superseded ABI tables); every
ref/harec/qbe cite, task cite, encoding/ELF contract, and rule-10
twin pointer kept; lost lifetime/rationale lines restored where the
sweep over-cut (elf_globals ownership, kwtab linear-scan). Comment-
only proven: all five wwstage tool binaries byte-identical across
the sweep; test-commit, test-byteid (161+1399, 0 pinned-divergent),
and test-bootstrap (fixed point + 991-995 byte-id) all exit 0.
The read-through banked 66 latent-bug leads (checkpoint).

cmd/wcc/ast.c

@@ -1,9 +1,5 @@
 /*
- * ast.c — Node constructor + s-expression printer.
- *
- * Constructor zeroes everything past kind/pos. Printer is rigid and
- * deterministic so golden tests can diff. One node per logical line,
- * children indented by 2 spaces.
+ * Printer output is rigid and deterministic so golden tests can diff.
  */
 #include "ww.h"
 #include <string.h>