feat: add 4 universal skills from cli-ai-skills

- Add audio-transcriber skill (v1.2.0): Transform audio to Markdown with Whisper
- Add youtube-summarizer skill (v1.2.0): Generate summaries from YouTube videos
- Update prompt-engineer skill: Enhanced with 11 optimization frameworks
- Update skill-creator skill: Improved automation workflow

All skills are zero-config, cross-platform (Claude Code, Copilot CLI, Codex)
and follow Quality Bar V4 standards.

Source: https://github.com/ericgandrade/cli-ai-skills

skills/youtube-summarizer/scripts/extract-transcript.py

@@ -0,0 +1,65 @@
+#!/usr/bin/env python3
+"""
+Extract YouTube video transcript
+Usage: ./extract-transcript.py VIDEO_ID [LANGUAGE_CODE]
+"""
+
+import sys
+from youtube_transcript_api import YouTubeTranscriptApi, TranscriptsDisabled, NoTranscriptFound
+
+def extract_transcript(video_id, language='en'):
+    """Extract transcript from YouTube video"""
+    try:
+        # Try to get transcript in specified language with fallback to English
+        transcript = YouTubeTranscriptApi.get_transcript(
+            video_id,
+            languages=[language, 'en']
+        )
+        
+        # Combine all transcript segments
+        full_text = " ".join([entry['text'] for entry in transcript])
+        return full_text
+        
+    except TranscriptsDisabled:
+        print(f"❌ Transcripts are disabled for video {video_id}", file=sys.stderr)
+        sys.exit(1)
+    except NoTranscriptFound:
+        print(f"❌ No transcript found for video {video_id}", file=sys.stderr)
+        sys.exit(1)
+    except Exception as e:
+        print(f"❌ Error: {e}", file=sys.stderr)
+        sys.exit(1)
+
+def list_available_transcripts(video_id):
+    """List all available transcripts for a video"""
+    try:
+        transcript_list = YouTubeTranscriptApi.list_transcripts(video_id)
+        print(f"✅ Available transcripts for {video_id}:")
+        
+        for transcript in transcript_list:
+            generated = "[Auto-generated]" if transcript.is_generated else "[Manual]"
+            translatable = "(translatable)" if transcript.is_translatable else ""
+            print(f"  - {transcript.language} ({transcript.language_code}) {generated} {translatable}")
+        
+        return True
+    except Exception as e:
+        print(f"❌ Error listing transcripts: {e}", file=sys.stderr)
+        return False
+
+if __name__ == "__main__":
+    if len(sys.argv) < 2:
+        print("Usage: ./extract-transcript.py VIDEO_ID [LANGUAGE_CODE]")
+        print("       ./extract-transcript.py VIDEO_ID --list  (list available transcripts)")
+        sys.exit(1)
+    
+    video_id = sys.argv[1]
+    
+    # Check if user wants to list available transcripts
+    if len(sys.argv) > 2 and sys.argv[2] == "--list":
+        list_available_transcripts(video_id)
+        sys.exit(0)
+    
+    # Extract transcript
+    language = sys.argv[2] if len(sys.argv) > 2 else 'en'
+    transcript = extract_transcript(video_id, language)
+    print(transcript)