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/hyperlink_route.rs

@@ -124,8 +124,6 @@ mod tests {
         TerminalContext::default()
     }
 
-    // -- hyperlink_skip_reason tests --
-
     #[test]
     fn apple_terminal_skip_reason() {
         assert_eq!(
@@ -199,8 +197,6 @@ mod tests {
         assert_eq!(ctx.hyperlink_skip_reason(), Some("vte_old"));
     }
 
-    // -- resolve_hyperlink_route tests --
-
     #[test]
     fn iterm2_emits_osc8() {
         let route = resolve_hyperlink_route(&iterm2_ctx());