Migrate to ROS 2 Jazzy + Gazebo Harmonic with native pixi workflow

[matejstastny]

THT-392

Summary

• Migrates from ROS 2 Humble + Gazebo Fortress to ROS 2 Jazzy + Gazebo Harmonic
• Adds sim native <robot> command via pixi — self-contained, works on Linux/macOS/WSL2, no system pollution
• Updates Dockerfile + Dev Container to Jazzy/Harmonic (Docker workflow unchanged)
• Updates all docs to present native pixi as the primary workflow and Docker as the alternative

Test plan

• pixi install completes without errors
• pixi run sim native arm launches Gazebo + RViz + Joint GUI
• sim docker arm still works inside the Dev Container
• Docs site builds (npm run build in docs/) and looks good

[CPrutean]

Looks good to me, good work moving to a newer version but something needs to be done about the lock file....

[RadAlpaca11]

Works for me!