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-shell/src/sampling/mod.rs

@@ -2,30 +2,17 @@ pub mod conversation;
 pub mod error;
 pub mod types;
 
-// `Client` is the legacy alias used throughout the shell. A later refactor
-// retired the bespoke shell HTTP client and points `Client` at the sampler crate's
-// `SamplingClient` -- the two have identical method sets, so call-sites
-// compile unchanged.
 pub use self::conversation::*;
 pub use self::error::{ResponseModelMetadata, Result, SamplingError};
 pub use self::types::*;
 pub use kigi_sampler::ApiBackend;
 pub use kigi_sampler::SamplingClient as Client;
 
-// Re-export async-openai Responses API types under `rs` namespace
 pub use async_openai::types::responses as rs;
 
-// ---------------------------------------------------------------------------
-// kigi-sampler re-exports
-// ---------------------------------------------------------------------------
-//
-// The actual streaming / retry / HTTP-client logic lives in the
-// `kigi-sampler` crate. We re-export the public surface here so
-// `crate::sampling::{SamplerHandle, SamplerConfig, ...}` paths keep working
-// for callers that haven't been ported to spell these directly via
-// `kigi_sampler::*`. The shell-side `sampling::client::Config`
-// composite was removed when its only remaining role -- session-snapshot
-// state for `MvpAgent` -- was migrated to `RefCell<SamplerConfig>` directly.
+// The streaming / retry / HTTP-client logic lives in `kigi-sampler`; these
+// re-exports keep `crate::sampling::{SamplerHandle, SamplerConfig, ...}` paths
+// working for callers not yet ported to `kigi_sampler::*` directly.
 pub use kigi_sampler::{
     InferenceLatencyStats, OriginClientInfo, RequestId, SamplerActor, SamplerConfig, SamplerHandle,
     SamplingChannel, SamplingClient, SamplingErrorInfo, SamplingErrorKind, SamplingEvent,