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-pager-render/src/terminal/overlay.rs

@@ -11,6 +11,9 @@ use super::image::{
 static NEXT_OWNER_ID: AtomicU64 = AtomicU64::new(1);
 
 thread_local! {
+    /// Owner whose image the terminal is believed to still hold; a matching
+    /// owner lets the next frame re-place that image without retransmitting
+    /// its pixel data.
     static OWNER: std::cell::Cell<Option<u64>> = const { std::cell::Cell::new(None) };
 }
 
@@ -20,6 +23,10 @@ pub(crate) enum Ownership {
     Clear,
 }
 
+/// Escape bytes plus the ownership transition they imply. The transition is
+/// applied only by [`Escapes::commit`] or [`PostFlush::write_to`], so escapes
+/// that are built and then dropped — or that fail to reach the terminal —
+/// leave `OWNER` describing what the terminal actually holds.
 #[derive(Debug)]
 pub struct Escapes {
     bytes: String,