Add per-indexer ratio-based seeding policy

Introduce a per-indexer ratioLimit alongside seedingTimeMinutes to control torrent cleanup. Updates include: documentation (scheduler and settings pages), types and API (saved indexer config now includes ratioLimit), setup and management UI (new TorrentSeedingFields component, modal wiring, validation and handlers), and processor logic (cleanup-seeded-torrents now requires AND-semantics between time and ratio; 0 disables a criterion, both 0 = never cleaned, undefined client ratio with ratioLimit>0 = not met). Tests were added/updated to cover ratio-only, time+ratio, missing-ratio, and UI interactions. Default behavior: ratioLimit defaults to 0 (no ratio requirement).

tests/app/setup/steps/ProwlarrStep.test.tsx

@@ -15,6 +15,7 @@ const indexersMock = [
     name: 'Indexer',
     priority: 10,
     seedingTimeMinutes: 0,
+    ratioLimit: 1.5,
     rssEnabled: true,
     categories: [],
   },