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-shell/src/extensions/feedback.rs

@@ -97,7 +97,6 @@ async fn handle_feedback(agent: &MvpAgent, args: &acp::ExtRequest) -> ExtResult
                 match serde_json::from_str::<ClientFeedbackInput>(args.params.get()) {
                     Ok(input) => input,
                     Err(_) => {
-                        // Fallback: parse simple FeedbackRequest from /feedback command
                         let simple: crate::session::FeedbackRequest = parse_params(args)?;
                         ClientFeedbackInput {
                             session_id: simple.session_id,
@@ -173,7 +172,6 @@ async fn handle_feedback(agent: &MvpAgent, args: &acp::ExtRequest) -> ExtResult
                 }
             }
 
-            // Track rating in session signals
             if let (Some(session_handle), Some(rating_value)) =
                 (&session_handle, feedback_input.rating_value)
             {
@@ -193,7 +191,6 @@ async fn handle_feedback(agent: &MvpAgent, args: &acp::ExtRequest) -> ExtResult
                 }
             }
 
-            // Log feedback type for debugging
             if feedback_input.is_solicited() {
                 tracing::info!(
                     session_id = %feedback_input.session_id,