Add new i18n keys to language files

Add new localization keys across multiple ytsage language JSONs. Common addition: "filter_playlist_placeholder" added to most languages. Spanish, Turkish and Chinese receive several new strings for custom commands, proxy settings, FFmpeg installation messages, history loading, time/placeholders and validation messages. Also ensure files end with newline. Files modified: ar, de, es, fr, hi, id, it, ja, pl, pt, ru, tr, zh.

ytsage/languages/hi.json

@@ -96,7 +96,8 @@
     "filter_languages_placeholder": "भाषाएं फ़िल्टर करें (जैसे: hi, en)...",
     "no_subtitles_available": "कोई उपशीर्षक उपलब्ध नहीं",
     "matching": "मेल खाता",
-    "ytdlp_log_title": "yt-dlp लॉग"
+    "ytdlp_log_title": "yt-dlp लॉग",
+    "filter_playlist_placeholder": "Filter videos..."
   },
   "tabs": {
     "cookies": "कुकीज़ के साथ लॉगिन",
@@ -637,4 +638,4 @@
     "update_failed": "❌ अपडेट विफल: {error}",
     "check_failed": "अपडेट की जांच विफल। कृपया अपना इंटरनेट कनेक्शन जांचें।"
   }
-}
+}