Publishing OrchestKit to the official MCP registry

This PR adds server.json at the repo root — the manifest the mcp-publisher CLI reads to list OrchestKit's remote MCP server in registry.modelcontextprotocol.io (the canonical directory other catalogs pull from). Closes part of orank "Listed in MCP registries".

{
  "name": "io.github.yonatangross/orchestkit",
  "title": "OrchestKit Docs MCP",
  "remotes": [{ "type": "streamable-http",
    "url": "https://orchestkit.yonyon.ai/api/mcp" }]
}

Owner step (GitHub-namespace auth — can't be automated)

1. brew install mcp-publisher (or download the release)

2. mcp-publisher login github — proves you own github.com/yonatangross (the io.github.yonatangross/* namespace)

3. mcp-publisher publish from the repo root

The server is already live + verified at /api/mcp (Streamable HTTP, read-only tools). No code change — just the registry manifest.