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-codebase-graph/src/scope_graph/edges.rs

@@ -2,21 +2,21 @@
 
 use serde::{Deserialize, Serialize};
 
-/// Describes the relation between two nodes in the ScopeGraph.
+/// Edge weight in the ScopeGraph. Every variant is directed source-to-target,
+/// in the order its name reads.
 #[derive(Serialize, Deserialize, PartialEq, Eq, Copy, Clone, Debug)]
 pub enum EdgeKind {
-    /// The edge weight from a nested scope to its parent scope.
+    /// Nested scope to its parent scope.
     ScopeToScope,
 
-    /// The edge weight from a definition to its definition scope.
+    /// Definition to the scope that owns it, which for a hoisted def is the
+    /// parent of the scope it was written in.
     DefToScope,
 
-    /// The edge weight from an import to its definition scope.
+    /// Import to its defining scope.
     ImportToScope,
 
-    /// The edge weight from a reference to its definition.
     RefToDef,
 
-    /// The edge weight from a reference to its import.
     RefToImport,
 }