perf(tui): render streaming token secara inkremental + kurangi redraw sia-sia

- fix(view): token streaming kini benar-benar tampil — sebelumnya cache
  display_lines tidak pernah di-rebuild saat pesan terakhir berubah
  (msg_count == cached_count), jadi teks AI streaming tidak pernah muncul
  sampai pesan baru/resize
- perf(view): streaming kini hanya re-render pesan TERAKHIR (splice di
  batas cached_last_start) → O(konten baru) per token, bukan O(seluruh
  history); guard cached_last_len mencegah re-render pada frame spinner
  tanpa token baru
- perf(run): skip chrono::Utc::now() + drain toasts saat tidak ada toast
- perf(misc): drain_expired_toasts tidak lagi clone seluruh daftar toast
- perf(view): render_toasts fast-path saat toasts kosong

apps/interfaces/tui/src/run.rs

@@ -112,9 +112,12 @@ fn run_loop_inner(
         }
 
         // Drain expired toasts exactly once per loop iteration (was being
-        // done here AND in Action::Tick before this fix).
-        let now_ms = chrono::Utc::now().timestamp_millis();
-        state.misc.drain_expired_toasts(now_ms);
+        // done here AND in Action::Tick before this fix). Skip the clock
+        // syscall + Vec scan when there are no toasts at all.
+        if !state.misc.toasts.is_empty() {
+            let now_ms = chrono::Utc::now().timestamp_millis();
+            state.misc.drain_expired_toasts(now_ms);
+        }
 
         // Skip render when nothing has changed — avoids expensive markdown
         // re-parse and layout recalculation every cycle while idle.