Artifact connector declarations accept "dynamic": true

What

A published artifact declares which connectors (MCP servers, the outside services Claude can reach) its page may call, under capabilities.mcp. That declaration has a new option:

• "dynamic": true lets the page call connectors the declaration does not list.
• With "dynamic": true, the "servers" list may be empty. Before, an empty list always failed with no_servers.
• Any dynamic value other than the JSON boolean true, or leaving it out, is refused with the new dynamic_not_boolean error.
• When a page calls servers the declaration does not list, the publish warning now says each viewer will be asked to approve them at first use, instead of saying the calls fail.
• The empty-servers error now ends "is refused" instead of "is always refused".

Why

Artifact authors no longer have to name every connector up front. Instead of a fixed list set at publish time, each viewer decides the first time the page uses a connector.