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-auth/src/retry_middleware.rs

@@ -1,5 +1,4 @@
 //! `reqwest-middleware` layer: stamps auth headers and retries on 401.
-//! Gated behind the `middleware` cargo feature.
 
 use std::sync::Arc;
 
@@ -52,6 +51,8 @@ impl Middleware for AuthRetryMiddleware {
         if resp.status() != StatusCode::UNAUTHORIZED || self.max_retries == 0 {
             return Ok(resp);
         }
+        // Streaming bodies do not clone, so such requests cannot be replayed
+        // and the 401 stands.
         let Some(backup) = backup else {
             return Ok(resp);
         };
@@ -154,7 +155,7 @@ mod tests {
         m.assert_async().await;
     }
 
-    /// Simulates a real auth manager: starts with stale token, refresh swaps to fresh.
+    /// Starts with a stale token; refresh swaps in the fresh one.
     struct SimulatedAuthManager {
         token: Mutex<Option<String>>,
         fresh_token: String,