MCP: add a file upload tool so AI agents can attach real files to records

Scope & Context The built-in MCP server (Agent API) exposes CRUD, actions, workflows, metadata, views, dashboards, webhooks, logic functions and roles — but no tool to upload a file. This makes the attachments object effectively read-only for AI agents: they can create the attachment *record*, but there is no way to get file bytes into the storage layer through MCP. The ticket is about adding an upload_file tool (ACTION category) to the MCP tool catalog, honoring the existing UPLOAD_FILE role permission flag. Use case: field-service CRM where external AI agents (Claude Code / Claude Desktop / any MCP client) prepare documents — generated PDFs, photos forwarded by a technician, scanned protocols — and need to attach them to a company, opportunity or custom-object record. Today this forces every MCP integration to also carry a REST/GraphQL client with a separately-managed auth path, just for the upload step. Current behavior Verified against a v2.37.0 workspace: • get_to…