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/src/ids.rs

@@ -11,7 +11,6 @@ use std::str::FromStr;
 
 use serde::{Deserialize, Deserializer, Serialize};
 
-/// Errors produced by id constructors and validators.
 #[derive(thiserror::Error, Debug, Clone, PartialEq, Eq)]
 pub enum IdError {
     #[error("identifier must not be empty")]
@@ -56,7 +55,6 @@ macro_rules! opaque_id {
         pub struct $name(String);
 
         impl $name {
-            /// Construct, validating the id's invariants.
             pub fn new(value: impl Into<String>) -> Result<Self, IdError> {
                 let value = value.into();
                 ensure_non_empty(&value)?;
@@ -132,7 +130,6 @@ opaque_id!(
 );
 
 impl ToolCallId {
-    /// Generate a fresh UUID v7-backed `ToolCallId`.
     pub fn new_v7() -> Self {
         Self(uuid::Uuid::now_v7().to_string())
     }
@@ -209,9 +206,6 @@ opaque_id!(
 
 /// Per-connection monotonic notification sequence (starts at 0 on every new
 /// connection).
-///
-/// The inner `u64` is private so `new`, `From<u64>`, and `Default` are the
-/// only construction paths.
 #[derive(
     Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord, Default, Serialize, Deserialize,
 )]