ci: add docker-compose interop harness (hiroz container <-> ROS 2 Jazzy)

[nargetdev]

Add a cross-container RED/GREEN test harness where hiroz runs in its own container (a Raspberry Pi analogue) and talks idiomatic zenoh through rmw_zenohd to a separate container with a full ROS 2 Jazzy install:

• compose/docker-compose.yml: three services (rmw_zenohd router, hiroz testbed, ROS 2 gate runner) on one bridge network with healthcheck-gated startup; multicast scouting disabled so tcp/router:7447 is the only rendezvous. HIROZ_PLATFORM=linux/arm64 switches the hiroz container to arm64 (cross-compiled with cargo-zigbuild, runtime under QEMU).
• crates/hiroz/examples/compose_testbed.rs: long-running multi-node testbed (talker, ping->pong echo, AddTwoInts server, retrying AddTwoInts client, Fibonacci action server, parameter node) mirroring the scenarios proven by hiroz-tests interop tests.
• compose/gates/: one bash gate per capability — topics both directions, services both directions, ros2 param list/get/set, fibonacci action goal/feedback/result plus graph introspection — with a GREEN/RED summary and aggregate exit code via --exit-code-from gates.
• .github/workflows/compose-interop.yml: builds both images with buildx (gha layer cache), runs the gates on PRs and main pushes, dumps logs on failure; workflow_dispatch input runs the Pi analogue as linux/arm64.

https://claude.ai/code/session_01ER6KMvKVGLBkdf8X5rNWNC

Description

Checklist

• Ran ./scripts/check-local.sh successfully
• Added/updated tests/documentation (if applicable)

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External contributors: Please open as draft initially. See CONTRIBUTING.md.

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