Complete Phase C (custom commands & yt-dlp updater) and Phase D (library, UX & notifications)

Phase C had been implemented in the working tree but never committed:
named custom-command templates (CRUD + per-download override), command
preview, and the in-app yt-dlp self-updater.

Phase D adds: history search/kind-filter/multi-select/bulk-delete/
re-download; native OS notifications on completion/failure; a private/
incognito download mode that skips history; settings+template backup/
restore via JSON; and a persistent error log surfaced as a Diagnostics
report in Settings.

See ROADMAP.md for the full per-item breakdown.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/main/history.ts

@@ -42,6 +42,13 @@ export function removeHistory(id: string): HistoryEntry[] {
   return entries
 }
 
+export function removeManyHistory(ids: string[]): HistoryEntry[] {
+  const remove = new Set(ids)
+  const entries = listHistory().filter((e) => !remove.has(e.id))
+  save(entries)
+  return entries
+}
+
 export function clearHistory(): HistoryEntry[] {
   save([])
   return []