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/ptyctl/src/keys.rs

@@ -45,7 +45,8 @@ fn parse_to_events(input: &str) -> Result<Vec<KeyEvent>> {
             // Try to parse a special key notation.
             let start_pos: String = chars.clone().collect();
             if let Some(end) = start_pos.find('>') {
-                let notation = &start_pos[1..end]; // between < and >
+                // between < and >
+                let notation = &start_pos[1..end];
                 // Consume chars including the >.
                 for _ in 0..=end {
                     chars.next();