docs(comments): rewrite comments across all crates to the guidelines

Sweep every first-party crate source (1956 .rs files) to the project comment
guidelines: delete redundant restatements, decorative banners, change
narration, and end-of-line comments; keep and tighten the crucial ones
(invariants, bug rationale, SAFETY blocks, ported-source attribution).

No functional code changed. Every edit is proven comment-only against the
prior tree by a comment-stripping lexer (string/char/raw-string aware) plus a
separate doctest-fence check. Where removing a comment made rustfmt or clippy
want to re-lay-out adjacent code, the minimal triggering comment is restored so
code tokens stay byte-identical.

Gates green: cargo fmt --all --check (0 diffs), cargo check and cargo clippy
--workspace --all-targets (0 warnings).

Adds scripts/check_codegen_comment_guidelines.py — the enforcement gate for
these guidelines (flags banners, end-of-line comments, change narration, and
commented-out code).

crates/codegen/kigi-tui/src/memory_release.rs

@@ -193,7 +193,8 @@ mod tests {
     #[serial_test::serial(MEMORY_RELEASE_DEFER)]
     fn deferred_request_coalesces_and_drains_once() {
         test_support::install_counting_hook();
-        run_deferred_release(); // drain any stale request
+        // Drain any stale request.
+        run_deferred_release();
 
         let before = test_support::calls();
         run_deferred_release();
@@ -204,7 +205,8 @@ mod tests {
         );
 
         request_release_after_draw();
-        request_release_after_draw(); // coalesces
+        // Coalesces.
+        request_release_after_draw();
         assert_eq!(
             test_support::calls(),
             before,