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/app/effects/tests.rs

@@ -437,7 +437,6 @@ async fn persist_setting_type_mismatch_errors_compact_mode() {
         "error message must mention key + expected kind, got: {err}",
     );
 }
-/// Type-mismatch for `show_timestamps`.
 #[tokio::test]
 async fn persist_setting_type_mismatch_errors_show_timestamps() {
     use crate::settings::SettingValue;
@@ -449,7 +448,6 @@ async fn persist_setting_type_mismatch_errors_show_timestamps() {
         "error message must mention key + expected kind, got: {err}",
     );
 }
-/// Type-mismatch for `show_timeline`.
 #[tokio::test]
 async fn persist_setting_type_mismatch_errors_show_timeline() {
     use crate::settings::SettingValue;
@@ -460,7 +458,6 @@ async fn persist_setting_type_mismatch_errors_show_timeline() {
         "error message must mention key + expected kind, got: {err}",
     );
 }
-/// Type-mismatch for `simple_mode`.
 #[tokio::test]
 async fn persist_setting_type_mismatch_errors_simple_mode() {
     use crate::settings::SettingValue;