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-tui/src/app/dispatch/tests/session/lifecycle.rs

@@ -1846,7 +1846,6 @@ fn dashboard_stop_double_press_via_handle_key_closes_top_level() {
         "second Ctrl+X via handle_input must close the target agent (Issue 300 regression)",
     );
 }
-/// Top-level resolver round-trip via real AgentView.
 #[test]
 fn session_id_resolver_round_trip_top_level() {
     use crate::views::dashboard::{DashboardRowId, PersistedRowId, SessionIdResolver};
@@ -1864,7 +1863,6 @@ fn session_id_resolver_round_trip_top_level() {
     };
     assert!(resolver.resolve(&absent).is_none());
 }
-/// Subagent resolver round-trip.
 #[test]
 fn session_id_resolver_round_trip_subagent() {
     use crate::views::dashboard::{DashboardRowId, PersistedRowId, SessionIdResolver};