fix: a release its download client will not let Minstrel follow is held back, not taken every pass (#6176)

The Black Keys' Ohio Players was grabbed 40 times in a day. FabledExchange
already held the torrent under another category from before Minstrel took
the downloads over: the add answered "duplicate", which counted as added,
and Exchange's listing, filtered to Minstrel's category, never showed it.
Half an hour later the grab ended gone, and the next pass took it again.

- A duplicate add that the client does not list for Minstrel is not a
  grab: the release is held back for a day with the client's own reason
  (already downloading X (category)), and the search moves on. Forced,
  it is refused with that reason.
- A release that ends gone a second time within a week is held back for
  a day, whatever the cause.
- release_blocks gains the reason 'gone' (migration 0098), shown as
  "Held back: its download client lost track of it".

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

web/src/lib/api/types.ts

@@ -783,7 +783,7 @@ export type DownloadsPage = {
 export type ReleaseBlock = {
   info_hash: string;
   name: string;
-  reason: 'operator' | 'files' | 'import' | 'stalled';
+  reason: 'operator' | 'files' | 'import' | 'stalled' | 'gone';
   detail: string;
   blocked_at: string;
   // When a release given up on may be taken again; null is for good.

web/src/lib/components/wanted/BlockList.svelte

@@ -37,6 +37,7 @@
     if (b.reason === 'operator') return 'Set aside by you';
     if (b.reason === 'files') return 'Set aside for its files';
     if (b.reason === 'stalled') return 'Given up on: it would not finish';
+    if (b.reason === 'gone') return 'Held back: its download client lost track of it';
     return 'Refused on import';
   }