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/tests/test_summary_reasoning_effort.rs

@@ -47,8 +47,9 @@ fn read_summary(home: &std::path::Path, session_id: &str) -> serde_json::Value {
 
 /// A fresh session on a model with a configured reasoning effort must persist
 /// that effort in `summary.json` without any model/effort switch.
+// requires pre-built binary
 #[tokio::test]
-#[ignore] // requires pre-built binary
+#[ignore]
 async fn test_fresh_session_persists_reasoning_effort() {
     with_local_set(|| async {
         let server = MockInferenceServer::start()
@@ -90,8 +91,9 @@ reasoning_effort = "high"
 
 /// A fresh session on a model with no configured effort must not invent one:
 /// `summary.json` omits the field (the model uses its server-side default).
+// requires pre-built binary
 #[tokio::test]
-#[ignore] // requires pre-built binary
+#[ignore]
 async fn test_fresh_session_without_effort_omits_field() {
     with_local_set(|| async {
         let server = MockInferenceServer::start()