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/benches/render.rs

@@ -23,11 +23,9 @@ use kigi_tui::theme::Theme;
 
 static BENCH_MD: &str = include_str!("bench.md");
 
-/// Viewport dimensions for the benchmark.
 const VIEWPORT_WIDTH: u16 = 120;
 const VIEWPORT_HEIGHT: u16 = 50;
 
-/// How many lines to advance per step in full_scroll.
 const SCROLL_STEP: u16 = 10;
 
 /// Entry count for the reveal benchmarks. Approximates the ~3,200-entry
@@ -76,8 +74,6 @@ fn compute_layouts(
         .collect()
 }
 
-// ─── Benchmarks ────────────────────────────────────────────────────
-
 /// Render a single frame at scroll offset 0 (top of document).
 ///
 /// The per-frame baseline with no top clipping — only bottom-clipped.
@@ -152,11 +148,10 @@ fn bench_full_scroll(c: &mut Criterion) {
     let appearance = AppearanceConfig::default();
     let layouts = compute_layouts(&entries, &appearance);
 
-    // usize: scroll offset is usize in the render path.
     let total: usize = layouts
         .iter()
         .map(|l| l.height as usize + l.gap_after as usize)
-        .sum(); // heights + gaps
+        .sum();
     let max_scroll = total.saturating_sub(VIEWPORT_HEIGHT as usize);
 
     // Prime the wrap cache
@@ -271,8 +266,6 @@ fn bench_windowed_scroll(c: &mut Criterion) {
     g.finish();
 }
 
-// ─── Reveal (scrollback-search n/N navigation) ─────────────────────
-
 /// One paragraph of lorem-style body per entry (~1.7 KB), so the
 /// `REVEAL_ENTRIES`-entry corpus is on the order of the motivating session's
 /// searchable text (a few MB; the exact size is logged).