docs: add requirements.txt to examples missing dependencies

[imran-siddique]

Many example directories have .py files but no requirements.txt. Priority: agent-compliance/examples, agent-mesh/examples/00-registration-hello-world, agent-sre/examples, agent-os/examples/carbon-auditor, agent-hypervisor/examples. Read imports, list pip deps with pinned versions. Pick 3-5 dirs per PR.