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/views/overlay_list.rs

@@ -1,10 +1,10 @@
 //! Shared prompt-area list overlay: accent bar, bold title, and a
 //! scrollable single-line row list with a cursor.
 //!
-//! One source of truth for the row geometry that `/rewind`'s picker phase
-//! and `/jump` previously each kept in sync by hand across their render,
-//! hit-test, and height functions. Row *content* stays with the caller
-//! (a closure); this owns chrome, cursor styling, and the scroll window.
+//! One source of truth for the row geometry shared by `/rewind`'s picker
+//! phase and `/jump` across their render, hit-test, and height paths. Row
+//! *content* stays with the caller (a closure); this owns chrome, cursor
+//! styling, and the scroll window.
 
 use ratatui::buffer::Buffer;
 use ratatui::layout::Rect;
@@ -29,7 +29,6 @@ pub struct RowCtx {
     pub is_cursor: bool,
     /// Resolved row background (cursor rows get the visual-selection bg).
     pub row_bg: Color,
-    /// Width available for the row's content.
     pub content_width: u16,
 }
 
@@ -210,12 +209,15 @@ mod tests {
             len: 2,
             selected: 0,
         };
-        assert_eq!(two.height(40), 5); // title + 2 rows + padding
+        // title + 2 rows + padding
+        assert_eq!(two.height(40), 5);
         let many = ListOverlay {
             len: 30,
             selected: 0,
         };
-        assert_eq!(many.height(40), 18); // 15-row cap
-        assert_eq!(many.height(12), 8); // 60% screen cap
+        // 15-row cap
+        assert_eq!(many.height(40), 18);
+        // 60% screen cap
+        assert_eq!(many.height(12), 8);
     }
 }