Add ElevenLabs MCP (#125)

* feat: add ElevenLabs MCP for text-to-speech and audio processing

Add official ElevenLabs MCP integration to enable text-to-speech, voice cloning, audio processing, and transcription capabilities.

Changes:
- Add elevenlabs.json MCP configuration in new audio category
- Use uvx package manager (matches existing mysql-integration, logfire pattern)
- Configure environment variables for API key and optional output modes

The ElevenLabs MCP enables:
- Text-to-speech generation with natural AI voices
- Voice cloning and custom voice design
- Audio isolation and processing
- Sound effects generation
- Audio transcription with speaker identification

Follows existing uvx-based MCP pattern from:
- cli-tool/components/mcps/database/mysql-integration.json
- cli-tool/components/mcps/devtools/logfire.json

Attribution: Official ElevenLabs MCP (MIT License)
Repository: https://github.com/elevenlabs/elevenlabs-mcp

* docs: add audio category to CONTRIBUTING.md MCP list

Add audio/ category to MCP categories list in contributing guidelines
to reflect the new category introduced with elevenlabs-mcp integration.

CONTRIBUTING.md

@@ -130,6 +130,7 @@ MCPs provide external service integrations for Claude Code.
    ```
 
 3. **MCP Categories**
+   - `audio/` - Audio processing, text-to-speech, transcription services
    - `integration/` - GitHub, GitLab, Jira
    - `database/` - PostgreSQL, MySQL, MongoDB
    - `cloud/` - AWS, Azure, GCP services

cli-tool/components/mcps/audio/elevenlabs.json

@@ -0,0 +1,14 @@
+{
+  "mcpServers": {
+    "elevenlabs": {
+      "description": "Official ElevenLabs MCP for text-to-speech, voice cloning, audio processing, and transcription. Generate AI voices, design custom voices, isolate audio, create sound effects, and more.",
+      "command": "uvx",
+      "args": ["elevenlabs-mcp"],
+      "env": {
+        "ELEVENLABS_API_KEY": "<your-api-key>",
+        "ELEVENLABS_MCP_BASE_PATH": "~/Desktop",
+        "ELEVENLABS_MCP_OUTPUT_MODE": "files"
+      }
+    }
+  }
+}