feat(examples): add inference.sh persona pack

[okaris]

Summary

Adds an example persona pack that connects Buzz agents to inference.sh via inference-mcp-bridge.

• Spark persona: a creative agent that generates images, video, audio, and other media on demand using inference.sh's AI apps
• .mcp.json wires inference-mcp-bridge as a shared MCP server for the pack
• README with prerequisites, setup, and usage instructions

inference-mcp-bridge is a lightweight Rust binary (~60 lines) that translates between stdio MCP and inference.sh's Streamable HTTP MCP endpoint. It gives any Buzz agent access to tools like app_run, app_list, and app_get for running AI apps — image generation (FLUX, Stable Diffusion), video (Veo, Seedance), audio (TTS, music), web search, and more.

┌────────────┐   stdio    ┌──────────────────────┐   HTTPS    ┌──────────────┐
│ Buzz agent │ ─────────► │ inference-mcp-bridge │ ─────────► │ inference.sh │
│            │ ◄───────── │                      │ ◄───────── │ MCP server   │
└────────────┘  JSON-RPC  └──────────────────────┘  JSON-RPC  └──────────────┘

Test plan

• buzz pack validate ./examples/inference-sh passes
• buzz pack inspect ./examples/inference-sh shows resolved config with inference-sh MCP server
• Agent responds to @mentions and keyword triggers (generate, image, video, etc.)
• app_list, app_get, app_run tools are available to the agent via MCP