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/install-dependencies.sh

@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+# Install youtube-transcript-api dependency
+
+set -e
+
+echo "📦 Installing youtube-transcript-api..."
+
+if command -v pip3 &>/dev/null; then
+    pip3 install youtube-transcript-api
+    echo "✅ Installation complete using pip3!"
+elif command -v pip &>/dev/null; then
+    pip install youtube-transcript-api
+    echo "✅ Installation complete using pip!"
+else
+    echo "❌ Error: pip not found"
+    echo "Please install Python pip first:"
+    echo "  macOS: brew install python3"
+    echo "  Ubuntu/Debian: sudo apt install python3-pip"
+    echo "  Fedora: sudo dnf install python3-pip"
+    exit 1
+fi
+
+# Verify installation
+python3 -c "import youtube_transcript_api; print('✅ youtube-transcript-api is ready to use!')" 2>/dev/null || {
+    echo "⚠️  Installation completed but verification failed"
+    echo "Try running: python3 -c 'import youtube_transcript_api'"
+    exit 1
+}