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/tips/clear_detector.rs

@@ -115,7 +115,8 @@ mod tests {
     fn gradual_delete_fires_at_residue_threshold() {
         let mut d = ClearDetector::default();
         type_to(&mut d, 0, 30);
-        type_to(&mut d, 30, 6); // still above the residue threshold
+        // still above the residue threshold
+        type_to(&mut d, 30, 6);
         assert!(d.observe_user_edit(6, 5), "crossing into residue fires");
         // Peak was reset: continuing to delete must not re-fire.
         assert!(!d.observe_user_edit(5, 0));
@@ -131,7 +132,8 @@ mod tests {
     #[test]
     fn short_draft_never_fires() {
         let mut d = ClearDetector::default();
-        type_to(&mut d, 0, 19); // one below FIRE_PEAK_LEN
+        // one below FIRE_PEAK_LEN
+        type_to(&mut d, 0, 19);
         assert!(!d.observe_user_edit(19, 0));
     }
 

crates/codegen/kigi-tui/src/tips/ephemeral.rs

@@ -248,9 +248,12 @@ mod tests {
         let mut state = EphemeralTipState::default();
         assert!(state.show(tip("a", 2), &mut HashMap::new()));
         assert!(state.is_active());
-        assert!(!state.tick()); // 2 -> 1
-        assert!(!state.tick()); // 1 -> 0
-        assert!(state.tick()); // 0 -> expired, needs redraw
+        // 2 -> 1
+        assert!(!state.tick());
+        // 1 -> 0
+        assert!(!state.tick());
+        // 0 -> expired, needs redraw
+        assert!(state.tick());
         assert!(!state.is_active());
         assert!(state.line().is_none());
         assert!(!state.tick(), "empty slot ticks are no-ops");
@@ -273,8 +276,10 @@ mod tests {
         let mut state = EphemeralTipState::default();
         let mut counts = HashMap::new();
         let _ = state.show(tip("a", 3), &mut counts);
-        assert!(!state.tick()); // 3 -> 2
-        let _ = state.show(tip("a", 3), &mut counts); // refresh back to 3
+        // 3 -> 2
+        assert!(!state.tick());
+        // refresh back to 3
+        let _ = state.show(tip("a", 3), &mut counts);
         for _ in 0..3 {
             assert!(!state.tick());
         }

crates/codegen/kigi-tui/src/tips/render.rs

@@ -104,7 +104,8 @@ mod tests {
         buf.set_string(0, 0, "XXXXXXXX", Style::default());
         buf.set_string(0, 1, "XXXXXXXX", Style::default());
 
-        let line = Line::from("0123456789"); // wider than the rect
+        // Wider than the rect.
+        let line = Line::from("0123456789");
         render_ephemeral_tip(area, &mut buf, &line);
 
         assert_eq!(row_text(&buf, area, 0), "01234567", "truncated at width");