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/memory_cmd.rs

@@ -106,7 +106,8 @@ fn run_clear(storage: &MemoryStorage, targets: &[ClearTarget], skip_confirm: boo
                 cleared = true;
                 println!("  Cleared: {}", t.label);
             }
-            Ok(false) => {} // nothing to clear for this scope
+            // Nothing to clear for this scope.
+            Ok(false) => {}
             Err(e) => {
                 errors.push(format!("{}: {e}", t.label));
             }