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-hunk-tracker/src/handle.rs

@@ -68,7 +68,6 @@ impl HunkTrackerHandle {
             .send(HunkTrackerCommand::HandleFileDeleted { path });
     }
 
-    /// Refresh git dirty cache.
     pub fn refresh_git_dirty_cache(&self) {
         let _ = self.cmd_tx.send(HunkTrackerCommand::RefreshGitDirtyCache);
     }
@@ -140,7 +139,6 @@ impl HunkTrackerHandle {
         reply_rx.await.unwrap_or_else(|_| Ok(vec![]))
     }
 
-    /// Get all hunks.
     pub async fn get_all_hunks(&self) -> Vec<Arc<Hunk>> {
         let (reply_tx, reply_rx) = oneshot::channel();
         let _ = self
@@ -169,7 +167,6 @@ impl HunkTrackerHandle {
         reply_rx.await.unwrap_or_default()
     }
 
-    /// Get hunks by source.
     pub async fn get_hunks_by_source(&self, source: HunkSourceFilter) -> Vec<Arc<Hunk>> {
         let (reply_tx, reply_rx) = oneshot::channel();
         let _ = self.cmd_tx.send(HunkTrackerCommand::GetHunksBySource {
@@ -293,7 +290,7 @@ impl HunkTrackerHandle {
         reply_rx.await.ok()
     }
 
-    /// Restore a previously snapshotted state. Replaces all current file
+    /// Restore a earlier snapshotted state. Replaces all current file
     /// states, turn index, and session stats in the actor.
     ///
     /// This is fire-and-forget — doesn't wait for processing.