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-fast-worktree/src/db/mod.rs

@@ -138,7 +138,7 @@ impl WorktreeDb {
             .with_context(|| format!("failed to open worktree DB: {}", path.display()))?;
         let db = Self { conn };
         db.set_journal_mode(journal_mode)?;
-        // Normal statement timeout, now that the conversion budget is done.
+        // Normal statement timeout, because the conversion budget is done.
         db.conn
             .busy_timeout(std::time::Duration::from_millis(5000))?;
         db.init_schema()?;

crates/codegen/kigi-fast-worktree/src/db/queries.rs

@@ -166,6 +166,7 @@ pub fn list(conn: &Connection, filter: &ListFilter) -> Result<Vec<WorktreeRecord
     }
     sql.push_str(" ORDER BY created_at DESC");
 
+    // Push order must match the ?N numbering handed out by the clauses above.
     let mut params: Vec<&dyn rusqlite::types::ToSql> = Vec::with_capacity(idx);
     if let Some(ref s) = status_str {
         params.push(s);

crates/codegen/kigi-fast-worktree/src/db/tests.rs

@@ -68,7 +68,8 @@ fn unregister_by_id() {
 
     assert!(db.unregister("a").unwrap());
     assert!(db.get("a").unwrap().is_none());
-    assert!(!db.unregister("a").unwrap()); // second call returns false
+    // second call returns false
+    assert!(!db.unregister("a").unwrap());
 }
 
 #[test]
@@ -629,7 +630,7 @@ fn network_mode_uses_fresh_per_host_truncate_db() {
 
     let db = WorktreeDb::open_at_with_journal_mode(&path, JournalMode::Truncate).unwrap();
     assert_eq!(journal_mode(&db), "truncate");
-    // Fresh per-host DB: legacy rows are intentionally not visible.
+    // Fresh per-host DB: legacy rows are deliberately not visible.
     assert!(db.get("wt-legacy").unwrap().is_none());
     db.register(&make_record("wt-nfs", "/tmp/wt-nfs", WorktreeKind::Manual))
         .unwrap();