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/app_view.rs

@@ -35,7 +35,6 @@ impl NewWorktreeDialogState {
             label_input: String::new(),
         }
     }
-    /// Handle a key event. Returns the dialog outcome.
     pub fn handle_key(&mut self, key: &crossterm::event::KeyEvent) -> NewWorktreeDialogOutcome {
         use crossterm::event::{KeyCode, KeyModifiers};
         if key.modifiers.contains(KeyModifiers::CONTROL)
@@ -1248,7 +1247,7 @@ impl AppView {
     }
     /// Reconcile the shared prompt queue for a session from a
     /// `kigi/queue/changed` broadcast. The broadcast is
-    /// authoritative: it fully replaces the previously-known queue for that
+    /// authoritative: it fully replaces the last-known queue for that
     /// session. An empty list clears the entry.
     ///
     /// Returns `(old_id, new_id)` for echoes retired via the kind+text