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-http/src/lib.rs

@@ -56,7 +56,7 @@ static CLIENT_TYPE: OnceLock<ClientType> = OnceLock::new();
 // `OriginClientInfo` is owned by `kigi-sampler` so `SamplerConfig` can use
 // it without taking a circular dependency on `kigi-shell`. Re-exported
 // under the same path (`crate::http::OriginClientInfo`) so existing call-sites
-// compile unchanged. The telemetry engine in `kigi-telemetry` consumes
+// compile `unchanged`. The telemetry engine in `kigi-telemetry` consumes
 // the same type via `kigi_sampler::OriginClientInfo`. The shell-specific
 // constructors that depended on `ClientType` (a shell-only type) are free
 // functions below.