Add MCP tool for managing registry configuration

[deepracticexs]

Summary

Currently there's no way to view or manage configured registries through MCP tools. When pushing a resource, users have to either remember the registry URL or set the RESOURCEX_REGISTRY environment variable manually. There's no discovery mechanism.

Proposal

Add MCP tools for registry management:

1. list-registries - Show all configured registries (from env, config file, or defaults)
2. set-default-registry - Set/update the default registry URL
3. registry-info - Show details about a specific registry (health, resource count, etc.)

Use Case

When working with Claude Code via MCP, the workflow is:

1. add a local resource
2. push to registry — but which registry? No way to check what's configured

Having a list-registries tool would let the AI agent discover the available registry before pushing, instead of requiring the user to manually provide the URL every time.

Example

# Current: user must know/provide the registry URL
push("my-resource:1.0.0", "https://registry.deepractice.dev")

# Proposed: agent can discover registries first  
list-registries() → [{ url: "https://registry.deepractice.dev", default: true }]
push("my-resource:1.0.0")  # uses default