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/auth.rs

@@ -2,8 +2,6 @@
 
 use super::*;
 
-// ── agent-bound kinds (bash) ─────────
-
 /// A bash command typed while a turn is RUNNING takes the
 /// server-authoritative immediate path (Effect + optimistic echo, no local
 /// queue entry).
@@ -23,9 +21,7 @@ fn bash_while_running_is_server_authoritative() {
         }
         other => panic!("expected immediate SendBashCommand, got {other:?}"),
     };
-    // Not in the local queue.
     assert_eq!(app.agents[&id].session.queue_len(), 0);
-    // Optimistic echo present with kind="bash".
     let q = app
         .shared_prompt_queue("test-session")
         .expect("echo present");
@@ -54,8 +50,8 @@ fn auth_complete_triggers_bundle_status_fetch() {
     );
 
     assert!(matches!(app.auth_state, AuthState::Done));
-    // Pager only refreshes the on-disk catalog snapshot; the actual
-    // bundle download now runs inside the shell post-auth.
+    // Pager only refreshes the on-disk catalog snapshot; the bundle
+    // download runs inside the shell post-auth.
     assert!(
         effects
             .iter()