feat: dynamic provider order, hoster routing, MKV sample fix

- Replace fixed primary/secondary/tertiary slots with unlimited ordered
  providerOrder: DebridProvider[] list; supports as many accounts as needed
- Provider list reorderable via up/down buttons in Accounts settings tab
- Migration: derives order from legacy primary/secondary/tertiary if empty
- Mega-Debrid split into megadebrid-api and megadebrid-web as separate providers
- Add per-hoster routing (hosterRouting) to assign specific debrid provider per hoster
- Fix duplicate MKV files in library: filter out sample files from Sample subfolders
- Remove legacy provider-selection dropdowns from hidden settings section
- Add CSS for provider-order-list/row/num/label/actions classes
- Update debrid tests: add providerOrder: [] to use legacy fallback path

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/main/constants.ts

@@ -59,6 +59,7 @@ export function defaultSettings(): AppSettings {
     linkSnappyPassword: "",
     archivePasswordList: "",
     rememberToken: true,
+    providerOrder: ["realdebrid", "megadebrid-api", "bestdebrid"],
     providerPrimary: "realdebrid",
     providerSecondary: "megadebrid-api",
     providerTertiary: "bestdebrid",