feat(bot): proactive cookie health-check + simpler user-facing errors

Add /cookies/check to youtube-downloader and instagram-downloader,
polled every 30 min from bot.py; alerts the admin bot on
healthy->broken transitions (with a 24h re-reminder cap while still
broken) and on recovery. Also stop leaking raw exception text to end
users - they now see a plain, friendly English message while the
admin bot still gets full technical detail via notify_admin_error.

instagram-downloader/app.py

@@ -200,6 +200,36 @@ def health():
     return jsonify({'status': 'ok', 'service': 'instagram-downloader'}), 200
 
 
+INSTAGRAM_COOKIE_TEST_URL = os.getenv(
+    'INSTAGRAM_COOKIE_TEST_URL',
+    'https://www.instagram.com/reel/Cvuh19eNWv_/'  # стабильный публичный ролик (NASA)
+)
+
+
+@app.route('/cookies/check', methods=['POST'])
+def cookies_check():
+    """Проверяет, рабочие ли сейчас Instagram cookies (для проактивного мониторинга)."""
+    cookies_file = Path(os.getenv('INSTAGRAM_COOKIES_FILE', 'instagram_cookies.txt'))
+    if not cookies_file.exists():
+        return jsonify({'cookies_present': False, 'cookies_valid': None,
+                         'detail': 'cookies file missing'}), 200
+
+    ydl_opts = {
+        'quiet': True,
+        'no_warnings': True,
+        'socket_timeout': 20,
+        'cookiefile': str(cookies_file.absolute()),
+        'http_headers': {'Referer': 'https://www.instagram.com/'},
+    }
+    try:
+        with yt_dlp.YoutubeDL(ydl_opts) as ydl:
+            ydl.extract_info(INSTAGRAM_COOKIE_TEST_URL, download=False)
+        return jsonify({'cookies_present': True, 'cookies_valid': True, 'detail': ''}), 200
+    except Exception as e:
+        return jsonify({'cookies_present': True, 'cookies_valid': False,
+                         'detail': str(e)[-500:]}), 200
+
+
 @app.route('/download/stream', methods=['POST'])
 def download_stream():
     """Скачивает видео с Instagram и возвращает бинарные данные"""