Add aggregate cloud and agent-server clients

[neubig]

Summary

Add aggregate OpenHands, Agent Server, and Cloud clients plus shared cloud transport and device-flow helpers while preserving existing endpoint-client APIs.

Tracking

PR: #267

Dependencies

• Blocks OpenHands/agent-canvas#1648.
• Provides the shared client foundation required by OpenHands/agent-canvas#1800.

PR evidence acceptance criteria

• Current main evidence: Compile and run a small client harness on current main that needs aggregate OpenHands, Agent Server, Cloud, transport, and device-flow helpers; show which APIs are unavailable while existing endpoint clients still work.
• PR branch evidence: Run the same harness on the PR branch against live endpoints and verify aggregate and legacy endpoint clients produce equivalent requests, device flow completes, and transport errors propagate correctly.
• Required evidence package: The PR records both commit SHAs and exact environment/setup. Run the full relevant backend, service, infrastructure, or data pipeline live with PR code and attach commands plus output/logs; a movie or video is not a substitute for this live run. Include npm build/test output, the harness, sanitized HTTP traces, and endpoint versions.