Add concurrent connections i18n keys

Add new i18n keys "concurrent_fragments" and "concurrent_fragments_help" to multiple language JSON files (ar, de, en, es, fr, hi, id, it, ja, pl, pt, ru, tr, zh). These expose a UI option for the number of concurrent connections per download with a help string (default: 1, warns about throttling/temporary blocks). Strings were added in English across locales and may need translation.

ytsage/languages/en.json

@@ -331,6 +331,8 @@
     "audio_normalization_help": "When enabled, audio tracks will be normalized. Note: This requires re-encoding, so a specific audio format (like MP3 or M4A) must be forced.",
     "filename_format": "Output Filename Format",
     "filename_format_help": "Available variables: %(title)s, %(uploader)s, %(upload_date)s, %(resolution)s, %(id)s, %(ext)s. Standard yt-dlp output template syntax is supported.",
+    "concurrent_fragments": "Concurrent Connections",
+    "concurrent_fragments_help": "Number of connections per download. Higher values bypass throttling but may cause temporary blocks if set too high. Default: 1.",
     "preferred_audio_format": "Preferred audio format:",
     "force_audio_format_help": "When enabled, audio-only downloads will be converted to your preferred format. This only applies when downloading audio formats.",
     "audio_format_best": "Best (No conversion)",
@@ -625,4 +627,4 @@
     "update_failed": "❌ Update failed: {error}",
     "check_failed": "Failed to check for updates. Please check your internet connection."
   }
-}
+}