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_index.json

@@ -404,6 +404,15 @@
     "risk": "unknown",
     "source": "unknown"
   },
+  {
+    "id": "audio-transcriber",
+    "path": "skills/audio-transcriber",
+    "category": "uncategorized",
+    "name": "audio-transcriber",
+    "description": "Transform audio recordings into professional Markdown documentation with intelligent summaries using LLM integration",
+    "risk": "safe",
+    "source": "unknown"
+  },
   {
     "id": "auth-implementation-patterns",
     "path": "skills/auth-implementation-patterns",
@@ -3910,8 +3919,8 @@
     "path": "skills/prompt-engineer",
     "category": "uncategorized",
     "name": "prompt-engineer",
-    "description": "Expert prompt engineer specializing in advanced prompting techniques, LLM optimization, and AI system design. Masters chain-of-thought, constitutional AI, and production prompt strategies. Use when building AI features, improving agent performance, or crafting system prompts.",
-    "risk": "unknown",
+    "description": "Transforms user prompts into optimized prompts using frameworks (RTF, RISEN, Chain of Thought, RODES, Chain of Density, RACE, RISE, STAR, SOAP, CLEAR, GROW)",
+    "risk": "safe",
     "source": "unknown"
   },
   {
@@ -4639,8 +4648,8 @@
     "path": "skills/skill-creator",
     "category": "uncategorized",
     "name": "skill-creator",
-    "description": "Guide for creating effective skills. This skill should be used when users want to create a new skill (or update an existing skill) that extends Claude's capabilities with specialized knowledge, workflows, or tool integrations.",
-    "risk": "unknown",
+    "description": "This skill should be used when the user asks to create a new skill, build a skill, make a custom skill, develop a CLI skill, or wants to extend the CLI with new capabilities. Automates the entire skill creation workflow from brainstorming to installation.",
+    "risk": "safe",
     "source": "unknown"
   },
   {
@@ -5669,6 +5678,15 @@
     "risk": "unknown",
     "source": "unknown"
   },
+  {
+    "id": "youtube-summarizer",
+    "path": "skills/youtube-summarizer",
+    "category": "uncategorized",
+    "name": "youtube-summarizer",
+    "description": "Extract transcripts from YouTube videos and generate comprehensive, detailed summaries using intelligent analysis frameworks",
+    "risk": "safe",
+    "source": "unknown"
+  },
   {
     "id": "zapier-make-patterns",
     "path": "skills/zapier-make-patterns",