docs: add agent instructions

[AntiD2ta]

Summary

• document environment setup, mock generation, and testing instructions for contributors

Testing

• go generate ./internal/compose ./internal/pkg/services ./internal/pkg/dependencies ./internal/monitoring ./internal/monitoring/locker ./internal/ui ./cli ./cli/actions
• go test ./... -count=1 -timeout 25m -skip TestE2E (fails: missing services and external RPCs)
• make format
• make format-check

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https://chatgpt.com/codex/tasks/task_e_6890d8f3baf88320b75a4a42d862fe9a