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-chat-state/src/actor/state.rs

@@ -137,7 +137,7 @@ pub(crate) struct ChatState {
     /// Opaque credential secrets (api key, optional extra auth, client version).
     /// Stored opaquely — the actor never interprets them.
     pub credentials: Credentials,
-    /// Bytes/4 estimate of tokens added since the last `record_token_usage`.
+    /// Bytes/4 estimate of tokens accumulated since the last `record_token_usage`.
     /// Used by `check_preflight_overflow` to detect context window overflows
     /// between model responses.
     pub estimated_tokens_since_model: u64,
@@ -304,7 +304,8 @@ mod tests {
     fn new_state_has_correct_defaults() {
         let state = ChatState::new(vec![], test_sampling_config());
         assert_eq!(state.prompt_index, 0);
-        assert_eq!(state.total_tokens, 0); // empty conversation → 0
+        // empty conversation → 0
+        assert_eq!(state.total_tokens, 0);
         assert!(state.conversation.is_empty());
         assert!(state.agent_edited_paths.is_empty());
         assert!(state.prompt_texts.is_empty());
@@ -333,7 +334,8 @@ mod tests {
             ConversationItem::tool_result("call-1", "w".repeat(4000).as_str()),
         ];
         let state = ChatState::new(items, test_sampling_config());
-        assert_eq!(state.total_tokens, 4000); // 4 * (4000/4)
+        // 4 * (4000/4)
+        assert_eq!(state.total_tokens, 4000);
     }
 
     #[test]