refactor: standardize delete return types to {id, success}

[qorexdev]

All delete* service functions now return { id: string; success: boolean } instead of boolean or void, matching the pattern from deleteComment.

• deleteAttachment: returns { id: entityId, success: true } via GraphQL entityId
• deleteDocument: returns { id, success: true } via GraphQL entity.id (fallback to input id)
• deleteIssueRelation: returns { id: entityId, success: true } (already had entityId in query)
• Updated documents delete command to pass the result directly to outputSuccess()
• Updated tests for all three services

Closes #85