feat: remove Tidal built-in provider, add extension download dedup/ISRC/Lyrics APIs, and expand l10n/a11y

Remove Tidal from built-in provider registry (metadata, search, download,
URL parsing) and delete tidal.go. Introduce extension runtime APIs for
lyrics lookup (getLyricsLRC), ISRC existence check (checkISRCExists), and
ISRC index management (addToISRCIndex). Refactor extension download response
construction into normalizeExtensionDownloadResult/overlayExtensionDownloadMetadata
helpers with AlreadyExists support and ISRC indexing. Switch download mirrors
to DoRequestWithUserAgent for ISP blocking detection. Add 50+ new
localization keys and accessibility labels across all supported locales.

ios/Runner/AppDelegate.swift

@@ -456,14 +456,6 @@ import Gobackend  // Import Go framework
             if let error = error { throw error }
             return response
 
-        case "getTidalMetadata":
-            let args = call.arguments as! [String: Any]
-            let resourceType = args["resource_type"] as! String
-            let resourceId = args["resource_id"] as! String
-            let response = GobackendGetTidalMetadata(resourceType, resourceId, &error)
-            if let error = error { throw error }
-            return response
-
         case "getProviderMetadata":
             let args = call.arguments as! [String: Any]
             let providerId = args["provider_id"] as! String
@@ -480,13 +472,6 @@ import Gobackend  // Import Go framework
             if let error = error { throw error }
             return response
 
-        case "convertTidalToSpotifyDeezer":
-            let args = call.arguments as! [String: Any]
-            let url = args["url"] as! String
-            let response = GobackendConvertTidalToSpotifyDeezer(url, &error)
-            if let error = error { throw error }
-            return response
-
         case "searchDeezerByISRC":
             let args = call.arguments as! [String: Any]
             let isrc = args["isrc"] as! String