fix(reader): the watched-channels list keeps its channels, its shares and its retries

- A channel someone follows: the videos its exploration brings in (the list's
  dialog, the channel page's explore) come in as the catalog's own, not
  flagged via_explore, which subscribing would never clear and which kept
  their watched marks waiting for good.
- The explore cleanup keeps the row of a channel a Takeout history shows
  watched (it still reclaims the videos), so a looked-at channel no longer
  drops off the list.
- The Shorts job takes up only users whose list still has lengths to ask or
  channels to name, by each user's own follows, blocks and dismissals; a
  naming that failed is tried again, and the list says it is not complete.
- The length lookups have a daily share of their own: a large history no
  longer leaves the export's Watch later file waiting a day.
- Only a channel of the user's own history can be put out of the list.
- The dialog's videos have a query root of their own: the list's
  invalidations no longer re-ask (and re-explore) under an open dialog.

frontend/src/lib/queryKeys.ts

@@ -38,7 +38,9 @@ export const qk = {
   channel: (id: string) => ["channel", id] as const,
   discoveredChannels: () => ["discovered-channels"] as const,
   watchedChannels: () => ["watched-channels"] as const,
-  watchedChannelVideos: (id: string) => ["watched-channels", "videos", id] as const,
+  // A root of its own, not under the list's: asking for them explores the channel (a write), so the
+  // list's invalidations must not refetch them under an open dialog.
+  watchedChannelVideos: (id: string) => ["watched-channel-videos", id] as const,
   blockedChannels: () => ["blocked-channels"] as const,
 
   // --- playlists ---