`mcp-publisher init` should prefer `mcpName` from `package.json`

[jonathanhefner]

Currently, mcp-publisher init copies information from package.json, if available. For example, it copies the name property:

https://github.com/modelcontextprotocol/registry/blob/18cde88a7e1c7916f1433c1f131a8de2fec8fe65/cmd/publisher/commands/init.go#L132-L143

However, in actuality, the server name must match the mcpName property, and is allowed to differ from the name property.

Therefore, mcp-publisher init should attempt to copy mcpName, and fall back to name if mcpName is not defined.