Keep Prowlarr results from distinct indexer entries separate (#1140)

Results were deduplicated on `guid` alone. When one tracker is
configured in Prowlarr as several indexer entries differing only by a
server-side search filter, all of them return the same guid for the same
torrent, so every entry but the first was silently discarded. Freeleech
and other filter-specific releases became invisible, replaced by the
unfiltered entry's copy, and which copy survived depended on query
ordering rather than user intent.

Include the indexer id in the dedup key so the entries stay distinct.

Release.source_id is qualified the same way. It keys the release cache
and becomes the download task id, so rows sharing a guid would otherwise
collide and a grab would route through whichever entry cached last,
defeating the point of showing them separately. The handler's task
matcher still accepts a bare guid or infoUrl so tasks queued before this
change still resolve.

Ordering now follows the priority already configured in Prowlarr (1-50,
lower preferred) rather than a new setting, since users curate that
ranking there and filtered entries are typically ranked ahead of their
unfiltered counterparts. The enabled-indexer list is fetched once and
reused for the enrichment check, so this costs no extra round trip.
Releases carry extra.indexer_priority, and the sort dropdown gains an
"Indexer priority" entry, ascending, alongside the existing alphabetical
"Indexer" sort; SortOption grew a default_direction for that, defaulting
to desc so "Peers" is unchanged.

PROWLARR_COLLAPSE_DUPLICATES (default off) optionally collapses a
release back to one row, resolved by the same Prowlarr priority. Left
off, every entry that carried a release keeps its own row, which is what
makes filtered results visible again.

Identity handling is defensive about partial payloads: a result that
cannot be identified is never dropped or merged, and collapse only
merges on a strong identifier (guid/downloadUrl/magnetUrl/infoUrl)
because merging on title alone would discard genuinely different
releases that share a name.

Fixes #1137

Co-authored-by: delize <4028612+delize@users.noreply.github.com>

docs/environment-variables.md

@@ -1211,6 +1211,7 @@ How long to cache individual book details. Default: 600 (10 minutes). Max: 60480
 | `PROWLARR_API_KEY` | Found in Prowlarr: Settings > General > API Key | string (secret) | _none_ |
 | `PROWLARR_INDEXERS` | Select which indexers to search. 📚 = has book categories. Leave empty to search all. | string (comma-separated) | _empty list_ |
 | `PROWLARR_AUTO_EXPAND` | Automatically retry search without category filtering if no results are found | boolean | `false` |
+| `PROWLARR_COLLAPSE_DUPLICATES` | Collapse a release that several indexer entries returned down to a single row. Leave this off to see every entry that carried it, which is what makes results from filter-specific entries (freeleech and the like) visible. | boolean | `false` |
 | `PROWLARR_USE_SEED_PREFERENCES` | Apply per-indexer seed time and ratio preferences from Prowlarr when sending torrents to the download client | boolean | `false` |
 
 <details>
@@ -1263,6 +1264,15 @@ Automatically retry search without category filtering if no results are found
 - **Type:** boolean
 - **Default:** `false`
 
+#### `PROWLARR_COLLAPSE_DUPLICATES`
+
+**Show one row per release**
+
+Collapse a release that several indexer entries returned down to a single row. Leave this off to see every entry that carried it, which is what makes results from filter-specific entries (freeleech and the like) visible.
+
+- **Type:** boolean
+- **Default:** `false`
+
 #### `PROWLARR_USE_SEED_PREFERENCES`
 
 **Use Prowlarr seed preferences**