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-pager-render/src/render/terminal_output.rs

@@ -258,7 +258,6 @@ fn first_param(params: &Params, default: u16) -> u16 {
     }
 }
 
-/// Map a 0-7 ANSI color index to a named ratatui color.
 fn ansi16(n: u16) -> Color {
     match n {
         0 => Color::Black,
@@ -272,7 +271,6 @@ fn ansi16(n: u16) -> Color {
     }
 }
 
-/// Map a 0-7 bright ANSI color index to a named ratatui color.
 fn ansi16_bright(n: u16) -> Color {
     match n {
         0 => Color::DarkGray,