MCP tool call failures now show why and who

Usage analytics for MCP tool calls now record two more details for failed calls: why the call failed and the name the MCP client identified itself with, even when the client is not a recognised integration.

• Failure reason is recorded for every failed MCP tool call, as the status code and error code the API returned.
• Client name is recorded as the client reports it, so unknown clients are no longer grouped as "other".