add-service-unit-test

Write a service-layer unit test in agent-manager-service (the Go control plane). Use when the user asks to add or fix a unit test for a service, mock a repository/client, or when CI lint fails on a test file (nilnil, goheader, exhaustruct, errorlint). Enforces the no-build-tag unit tier, moq-generated mocks, and the strict CI lint config that also lints test files.