feat: responsive pause/stop, non-blocking update with progress bar, delete saved sessions (1.5.0)

- carve: check cancellation inside chunks and per hit; reassembly stage is cancellable
- status exposes `stopping`; UI shows "Pausing…" immediately
- Tauri update commands run off the UI thread; download percentage reported
- delete autosaved sessions manually (one/all) and by retention setting
- chore(release): 1.5.0

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

crates/guara-core/tests/extras.rs

@@ -143,6 +143,7 @@ fn configuracoes_antigas_ganham_os_valores_padrao_novos() {
         notify: false,
         maps: true,
         updates: false,
+        ..Default::default()
     })
     .unwrap();
     let s = settings::load();