l4t infra fixes: aarch64 build args + robot-name resolution

[JohnYanxinLiu]

What features did you add and/or bugs did you address?

• Which GitHub issue does this address?

  No dedicated issue. This is a foundational infra PR extracted from Johnliu/optitrack emulation #367 (OptiTrack emulation) so the generic real-robot deployment fixes can be reviewed and merged first; Johnliu/optitrack emulation #367 is then rebased on top, shrinking its diff. It also unblocks the upcoming l4t (Jetson) profile work.

• Additional description if not fully described in the GitHub issue

  Two independent concerns, both generic (nothing OptiTrack-specific):

  1. aarch64 (Jetson/l4t, voxl) image builds

  • Dockerfile.robot: add ARG TARGET_ARCH=x86_64 and use it to parametrize LD_LIBRARY_PATH (.../lib/${TARGET_ARCH}-linux-gnu) so the arm64 images link against the correct arch triplet instead of the hard-coded x86_64.
  • Dockerfile.robot: install ros-${ROS_DISTRO}-mavros-extras (generic MAVROS dependency; also provides the vision_pose plugin used by external-pose deployments).
  • docker-compose.yaml: pass TARGET_ARCH: aarch64 to the voxl and l4t image builds.

  2. Robot name resolution ("robot launches with no name" bug)

  • .bashrc: honor a pre-set ROBOT_NAME (e.g. injected via docker compose) instead of always overriding it from the container/hostname mapping. The bws() flock build lock is retained.
  • default_robot_name_map.yaml: catch-all fallback maps to unknown_robot (a valid ROS namespace token) instead of unknown-robot (a hyphen makes the namespace invalid and launch fails).

• Please add videos and images to demonstrate the feature.

  N/A — build-arg + shell/config changes, no runtime UI.

How did you implement it?

• TARGET_ARCH defaults to x86_64, so the desktop/CI build is byte-for-byte unchanged; only the voxl/l4t services opt into aarch64.
• The name-resolution change is a guard (if [ -z "${ROBOT_NAME:-}" ]; then ... fi) wrapped around the existing container/hostname mapping block — no behavior change when ROBOT_NAME is unset.

How do you run and use it?

• Desktop (unchanged, sanity check the default arch path still builds):

  AUTOLAUNCH=false airstack up robot-desktop

• aarch64 image build (on a Jetson / arm64 host):

  airstack image-build --profile l4t robot-l4t

• Verify a pre-set ROBOT_NAME is honored:

  docker exec -e ROBOT_NAME=robot_1 <container> bash -lc 'echo $ROBOT_NAME'   # -> robot_1

Testing with PyTest

• No new pytests. This PR is infra/build plumbing; there is no runtime surface with a hermetic test hook. The existing build_packages / build_docker suites exercise the affected Dockerfile/compose.
• Command (optional, GPU runner): airstack test -m "build_docker or build_packages" -v
• Expected: robot images build; TARGET_ARCH default keeps the x86 build identical to develop.

Documentation

• Was mkdocs.yml updated? (y/n) n — no new module or user-facing doc page; changes are within existing docker/config files. CHANGELOG.md updated.
• Docs scope: existing multi-robot / docker docs remain accurate.
• Visual media: N/A.

Versioning

• Yes — bumped .env VERSION 0.19.0-alpha.5 → 0.19.0-alpha.6 per semantic versioning (trailing alpha label increment). CHANGELOG [Unreleased] updated.

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