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-system-power/src/linux.rs

@@ -17,7 +17,7 @@ const IFACE: &str = "org.freedesktop.login1.Manager";
 
 /// Linux listener handle.
 ///
-/// There is intentionally no clean stop: the worker thread parks on a blocking
+/// There is deliberately no clean stop: the worker thread parks on a blocking
 /// logind signal iterator, which cannot be interrupted without a signal
 /// arriving, so dropping this neither joins nor cancels it. The thread (and its
 /// D-Bus connection + sleep-delay inhibitor fd) live until process exit. That