MCP tools: service user and template management

[The127]

Summary

Add MCP tools for service user (M2M) management and email/message templates.

Depends on #232.

Tools

Service Users

Tool	API Endpoint	Description
create_service_user	POST /{vs}/users/service-users	Create service account
add_service_user_key	POST /{vs}/users/service-users/{id}/keys	Associate PEM public key + kid
remove_service_user_key	DELETE /{vs}/users/service-users/{id}/keys/{kid}	Remove a public key

Templates

Tool	API Endpoint	Description
list_templates	GET /{vs}/templates	List email/message templates
get_template	GET /{vs}/templates/{type}	Get template content by type

Notes

• Service user key operations require service_user:create / service_user:associate_key / service_user:remove_key permissions
• Template viewing is useful for AI agents helping debug email delivery issues