fix: skip GUI camera requests in server-only launches

[yeseorizi]

Problem

posim_robot.launch.py enables the ocean-waves GUI camera move even when gui:=false or headless:=true. There is no GUI camera service in that mode, so each run makes an unnecessary request and prints Service call timed out.

Change

Enable zoom_camera only for posim_ocean_waves and a non-server-only launch. One file changes. The existing GUI camera pose, delay, world and robot configuration remain unchanged.

Independent validation

Base: 23bb608a9a89b9cda3472792316a81711f1ce73e; fresh posim_demos overlay only. Linux ARM64 Docker on Apple M2, ROS 2 Lyrical / Gazebo Jetty. No input, plugin-shutdown or ros_gz overlay.

• LaunchContext matrix: ocean-waves / empty × GUI on/off × headless on/off — 8/8 expected conditions.
• Actual gui:=false headless:=false launch: no camera service request/timeout.
• Actual gui:=true headless:=true launch: no camera service request/timeout.
• Actual Gazebo GUI (gui:=true headless:=false, default 2 s delay), rendered via software OpenGL on Xvfb: automatic camera service returned data: true; /gui/camera/pose reported the requested position (-1, 0, 0.5). A subsequent camera move and restoration were confirmed by pose messages and screenshots.

The GUI test is Linux GUI in a virtual display, not native macOS/Metal. Stock ros_gz_bridge still segfaulted during teardown in these three standalone launches; this small camera-condition change neither includes nor claims the separate upstream shutdown fix.

Reproduce the affected path

ros2 launch posim_demos posim_robot.launch.py \
  namespace:=bluerov2 world_name:=posim_ocean_waves z:=-0.5 \
  paused:=false gui:=false headless:=true \
  use_teleop:=false use_web_joystick:=false

Before: camera request times out. After: no GUI camera request. With GUI enabled and headless disabled, the camera move is retained.

Please review; no merge or release is requested by this validation run.

CI infrastructure note (2026-10-08)

ARM64 run 37743089211 stopped in the runner-admin pre-job hook, before checkout/build: ~61.09 GiB free vs its 80 GiB minimum. This is not a compiler/test result for this change. No runner files, free-space thresholds, or maintenance hooks were changed. ARM64 CI remains unverified until the runner is ready; the Docker workflow does not publish PR images.