iii worker add mcp fails: hard dependency on unpublished skills worker

[orincolor]

Problem

Running iii worker add mcp always fails with a 422:

error: Failed to resolve worker graph: HTTP 422 Unprocessable Entity
{"error":{"available":[],"code":"worker_not_found","dependency_path":"mcp -> skills",
"fix":"Publish 'skills' or remove it from the dependency list.",
"message":"Worker 'skills' was not found in the registry.",
"requested":["^0.2.1"],"scope":"worker","worker":"skills"}}

The mcp worker declares a hard dependency on skills, but skills is not published in the registry and doesn't exist as runnable code in the repo — only as SKILL.md documentation files.

Impact

mcp is completely uninstallable.

Expected behavior

Either:

1. skills is published to the registry, or
2. The dependency is made optional — mcp works without skills (skills only adds MCP resources/prompts, tool invocation works standalone)

Environment

• iii v0.16.1
• macOS aarch64

[rohitg00]

Reated to #1723