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/ptyctl-cli/src/registry.rs

@@ -113,7 +113,8 @@ pub fn list_sessions() -> Result<Vec<(String, SessionInfo)>> {
                 .unwrap_or("")
                 .to_string();
             if name.starts_with('.') {
-                continue; // skip temp files
+                // skip temp files
+                continue;
             }
             if let Ok(json) = fs::read_to_string(&path)
                 && let Ok(info) = serde_json::from_str::<SessionInfo>(&json)