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-hunk-tracker/src/events.rs

@@ -6,7 +6,7 @@ use std::sync::Arc;
 
 use crate::types::{Hunk, HunkId, HunkLineInfo, HunkSource};
 
-/// Why a hunk was removed. Used by the LOC sink to decide whether to
+/// Why the tracker removed a hunk. Used by the LOC sink to decide whether to
 /// negate the hunk's accumulated LOC contribution.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
@@ -30,7 +30,7 @@ pub enum HunkEvent {
     /// A new hunk was created
     HunkAdded { path: PathBuf, hunk: Arc<Hunk> },
 
-    /// A hunk was removed.
+    /// A hunk stopped being tracked.
     HunkRemoved {
         path: PathBuf,
         hunk_id: HunkId,
@@ -69,6 +69,6 @@ pub enum HunkEvent {
     /// A file stopped being tracked (all hunks gone, not an agent file)
     FileRemoved { path: PathBuf },
 
-    /// Baseline was updated for a file (after accept or commit)
+    /// The tracker updated a file's baseline (after accept or commit)
     BaselineUpdated { path: PathBuf },
 }