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/wrap_cmd.rs

@@ -195,8 +195,6 @@ fn resolve_shell(shell: Option<&str>) -> String {
 /// the same; only the live outer→inner resize is not forwarded (see
 /// [`crate::pty_wrap::run_wrapped_command`]).
 fn should_wrap() -> bool {
-    // PTY wrapping requires native pseudo-terminal APIs (Unix openpty / Windows
-    // ConPTY), both of which `portable-pty` supports.
     if !cfg!(any(unix, windows)) {
         return false;
     }