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/auth.rs

@@ -11,10 +11,6 @@ use crate::app::app_view::{ActiveView, AppView, AuthMode, AuthState, PlatformLog
 use crate::scrollback::block::RenderBlock;
 use crate::scrollback::blocks::SessionEvent;
 
-// ---------------------------------------------------------------------------
-// Auth dispatch
-// ---------------------------------------------------------------------------
-
 /// `/logout` -- ask the shell to clear auth, then return to the login screen.
 pub(super) fn dispatch_logout(_app: &mut AppView) -> Vec<Effect> {
     vec![Effect::Logout]
@@ -45,7 +41,6 @@ pub(super) fn ensure_login_method(app: &mut AppView) {
     // No interactive method: leave login_method_id unset (fail-closed).
 }
 
-/// Error when no interactive login method is available (empty auth_methods).
 fn no_login_method_error(_app: &AppView) -> String {
     "No login method available".to_string()
 }