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-workspace/src/capability.rs

@@ -111,7 +111,7 @@ const _: () = assert!(
 
 /// Maps `(CapabilityMode, ToolKind)` -> kept-or-dropped.
 ///
-/// This `match` is intentionally exhaustive: when `ToolKind` gains a
+/// This `match` is deliberately exhaustive: when `ToolKind` gains a
 /// new variant the compiler errors here, forcing a triage decision.
 pub(crate) fn kind_allowed(mode: CapabilityMode, kind: ToolKind) -> bool {
     use CapabilityMode as M;
@@ -157,9 +157,7 @@ pub(crate) fn kind_allowed(mode: CapabilityMode, kind: ToolKind) -> bool {
     }
 }
 
-// ---------------------------------------------------------------------------
 // Tests
-// ---------------------------------------------------------------------------
 
 #[cfg(test)]
 mod tests {
@@ -285,9 +283,7 @@ mod tests {
         }
     }
 
-    // -----------------------------------------------------------------------
     // is_subset_of partial order
-    // -----------------------------------------------------------------------
 
     #[test]
     fn capability_mode_is_subset_of_reflexive() {