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-shell/src/managed_config.rs

@@ -92,7 +92,8 @@ pub fn clear_orphan() {
     }
     let home = crate::util::kigi_home::kigi_home();
     let Some(_lock) = try_lock_managed_config(&home) else {
-        return; // another process is syncing; retry next call
+        // another process is syncing; retry next call
+        return;
     };
     remove_managed_config_files(&home);
 }
@@ -313,7 +314,8 @@ fn managed_config_sync_interval() -> std::time::Duration {
 pub(crate) fn spawn_sync(cancel: tokio_util::sync::CancellationToken) {
     tokio::spawn(async move {
         let mut interval = tokio::time::interval(managed_config_sync_interval());
-        interval.tick().await; // skip immediate first tick
+        // skip immediate first tick
+        interval.tick().await;
 
         loop {
             tokio::select! {
@@ -805,7 +807,8 @@ fn purge_prior_tenant_on_identity_change() {
     };
     let home = crate::util::kigi_home::kigi_home();
     let Some(_lock) = try_lock_managed_config(&home) else {
-        return; // another process is mid-apply/remove; it owns the transition
+        // another process is mid-apply/remove; it owns the transition
+        return;
     };
     if crate::config::managed_config_identity_changed(Some(&team_id), None) {
         tracing::info!(team_id = %team_id, "identity changed; purging the prior tenant's managed config");