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-mcp/src/mcp_http_client.rs

@@ -135,13 +135,13 @@ impl ThrottleState {
 ///
 /// Backoff and episode state are per instance; the [`WarnBudget`] is the
 /// caller's, so a rebuilt client does not warn again within the cooldown.
+// No `Debug` derive: rmcp's `AuthClient` (an inner type) is not `Debug`.
 #[derive(Clone)]
 pub struct McpHttpClient<C> {
     inner: C,
     server_name: Arc<str>,
     state: Arc<parking_lot::Mutex<ThrottleState>>,
 }
-// No `Debug` derive: rmcp's `AuthClient` (an inner type) is not `Debug`.
 
 impl<C> McpHttpClient<C> {
     pub fn new(inner: C, server_name: impl Into<Arc<str>>, warn_budget: WarnBudget) -> Self {