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/common/kigi-tool-protocol/src/notification_wire.rs

@@ -16,7 +16,6 @@
 
 use serde::{Deserialize, Serialize};
 
-/// Adjacent-tagged notification wire wrapper.
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 #[serde(tag = "shape", content = "value", rename_all = "snake_case")]
 pub enum WireToolNotification {
@@ -72,9 +71,8 @@ pub const fn known_notification_kinds() -> &'static [&'static str] {
 }
 
 /// Reject custom notification kinds whose name shadows a known PascalCase
-/// variant. Runs at notification-emit time; an empty `kind` is accepted
-/// here (the producer is responsible for validating that the field is
-/// non-empty).
+/// variant. An empty `kind` is accepted here; the producer is responsible
+/// for validating that the field is non-empty.
 pub fn check_custom_kind(kind: &str) -> Result<(), KnownVariantCollision> {
     if KNOWN_NOTIFICATION_KINDS.contains(&kind) {
         Err(KnownVariantCollision {