Reclaim KV checkpoints the index cannot reach

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/app.rs

@@ -228,6 +228,8 @@ impl App {
                     // Before the counters are taken, so they measure what is
                     // actually reachable.
                     sweep_orphan_checkpoints(&kv_cache_path(), &projects);
+                    #[cfg(target_os = "macos")]
+                    crate::engine::sweep_transient_cache(&transient_cache_path());
                     let context_limit = preferences.context_tokens.max(0) as u32;
                     // Reopen on the project we left, with a fresh draft chat.
                     let last_project = preferences