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/scrollback/wrappers/mod.rs

@@ -43,7 +43,6 @@ mod tests {
     use ratatui::layout::Rect;
     use ratatui::style::Color;
 
-    /// Test that wrappers can be composed together.
     #[test]
     fn test_wrapper_composition() {
         let block = StubBlock::new("Hello", Color::Blue);
@@ -57,7 +56,6 @@ mod tests {
         // Padded: takes 3 columns (2+1), height unchanged
         assert_eq!(padded.desired_height(80), 3);
 
-        // Render and verify structure
         let area = Rect::new(0, 0, 20, 3);
         let mut buf = Buffer::empty(area);
         padded.render(area, &mut buf);