#1001 MCP server token kept when the server URL changes and not bound to the registered server

EARS: When a tenant re-registers an MCP server name with a different URL, the system shall drop the stored token unless a new one is supplied. When tools.mcp.call resolves an auth_secret_path, it shall send the token only to the URL registered with that secret. FOUND in #924 review (L6): api/mcp_registry.py POST upserts url and keeps tenants/<t>/mcp_<name> when auth_token is omitted; tools.mcp.call accepts any server_url with any auth_secret_path of the same tenant, so a workflow of that tenant can send the stored token to another URL. Bind: store the registered URL with the token (or look it up in highway.mcp_servers) and compare before sending.