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/tests/serde_roundtrip.rs

@@ -1002,9 +1002,9 @@ fn session_lifecycle_payloads_round_trip() {
 fn attach_route_round_trips_snake_case_and_tolerates_unknown() {
     assert_eq!(roundtrip(&AttachRoute::Local), json!("local"));
     assert_eq!(roundtrip(&AttachRoute::Remote), json!("remote"));
-    // "restored" was removed with restore-on-activity; old hubs may still send
-    // it, and it must fall into the tolerant `Unknown` bucket like any other
-    // retired/newer value.
+    // "restored" is a retired restore-on-activity route; old hubs may still
+    // send it, and it must fall into the tolerant `Unknown` bucket like any
+    // other retired/newer value.
     let parsed: AttachRoute =
         serde_json::from_value(json!("restored")).expect("tolerant parse of retired value");
     assert_eq!(parsed, AttachRoute::Unknown);