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).

src/app/setup/steps/ProwlarrStep.tsx

@@ -25,6 +25,7 @@ interface SelectedIndexer {
   protocol: string;
   priority: number;
   seedingTimeMinutes?: number; // Torrents only
+  ratioLimit?: number; // Torrents only (0 = no ratio requirement)
   removeAfterProcessing?: boolean; // Usenet only
   rssEnabled: boolean;
   audiobookCategories: number[]; // Categories for audiobook searches