feat(download): unsubscribed-show downloads from search

Episode search results gain d (download), D (delete), x (unsubscribe)
and enter (play for subscribed shows); downloads of unsubscribed shows
are recorded with the show's metadata under a deterministic synthetic
feed id and listed under an "Unsubscribed Show Downloads" section in
My Shows and the settings Download Manager. Classified at render time
by feed id or feed URL, so subscribing re-classifies the downloads and
unsubscribing purges them.

src/types/episode.ts

@@ -98,7 +98,9 @@ export enum DownloadStatus {
 export interface DownloadedEpisode {
   /** Episode ID */
   episodeId: string
-  /** Feed ID the episode belongs to */
+  /** Feed ID the episode belongs to. For downloads of shows that aren't
+   *  subscribed (search downloads) this is a deterministic synthetic id
+   *  ("unsub-<slug>") that also names the file subdirectory. */
   feedId: string
   /** Current download status */
   status: DownloadStatus
@@ -114,4 +116,16 @@ export interface DownloadedEpisode {
   fileSize: number
   /** Error message if failed */
   error: string | null
+  /** Episode title, persisted so unsubscribed-show downloads render without
+   *  a loaded feed. */
+  episodeTitle?: string
+  /** Audio URL, persisted so queued downloads survive a restart. */
+  audioUrl?: string
+  /** Publication date (ISO), for display of unsubscribed-show downloads. */
+  pubDate?: string
+  /** Show title, kept for downloads whose show isn't subscribed. */
+  podcastTitle?: string
+  /** The show's RSS feed URL, used to re-classify a download as subscribed
+   *  once the user subscribes to its show. */
+  podcastFeedUrl?: string
 }