The mcpcmd package was using the removed Cobra-style cli.Command API
(Use/Short/Long/RunE/StringFlag/AddCommand). Rewrites it to the current
core.Command{Description, Action, Flags} path-routed pattern so the
core-mcp binary compiles again. Registers both "mcp" and "mcp/serve"
for parity with the existing OnStartup service-mode flow.
Fixes the bridge DescribableGroup test that expected len == svc.Tools()
but ToolBridge.Describe prepends the GET tool-listing entry, so the
correct expectation is len + 1.
Co-Authored-By: Virgil <virgil@lethean.io>
91297d733d