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/dispatch/tests/status.rs

@@ -42,7 +42,6 @@ fn send_while_idle_with_nonempty_shared_queue_routes_to_server() {
             _ => None,
         })
         .unwrap_or_else(|| panic!("expected immediate SendPrompt for 'c', got {effects:?}"));
-    // Did NOT start a local turn or adopt "c" as the running prompt.
     assert!(
         !app.agents[&id].session.state.is_turn_running(),
         "must not promote 'c' to a local running turn"
@@ -220,8 +219,6 @@ fn show_usage_on_welcome_screen_is_noop() {
     );
 }
 
-// ── Minimal update-notice tests ──────────────────────────────────────
-
 #[test]
 fn minimal_update_notice_commits_a_system_block() {
     let mut app = test_app_with_agent();