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-agent-lifecycle/src/send/contributors/command.rs

@@ -10,7 +10,8 @@ pub struct CommandSpec {
 /// A parsed `/name args` invocation. The host owns parsing and routes it to the command's one owner.
 pub struct CommandInvocation<'a> {
     pub name: &'a str,
-    pub args: &'a str, // Whitespace-trimmed; empty for a bare `/name`.
+    // Whitespace-trimmed; empty for a bare `/name`.
+    pub args: &'a str,
 }
 
 /// What a handled command does to the turn; rejections travel as the `Err` reason.