Add Docker-based macOS workflow and headless CLI

[aalksii]

Summary

This PR makes Brickr much easier to run on modern macOS systems, especially Apple Silicon, by adding a Docker-based workflow and a headless CLI path.

Changes included:

• add a Docker-based setup for building and running Brickr on macOS
• expose the GUI through a browser-based noVNC desktop instead of relying on local X11 setup
• replace the bundled runtime binvox path with a Python voxelizer flow that works reliably in the container
• fix BINVOX dimension handling so generated voxel files load correctly
• improve file handling in the containerized/browser workflow
• add a headless CLI mode for converting meshes, printing stats, and exporting outputs without opening the GUI

Why

The original project is older and difficult to run on a modern macOS machine, particularly on Apple Silicon. The bundled Linux binvox binary also fails in this environment, which blocks mesh import.

This PR provides a practical path to keep the project usable today:

• Dockerized build/runtime
• browser-accessible GUI
• working mesh voxelization in-container
• CLI usage for scripting and non-interactive workflows

CLI Example

docker run --rm \
  --platform=linux/amd64 \
  --entrypoint /opt/brickr/brickr \
  -e BINVOX_PATH=/opt/brickr/tools/obj_to_binvox.py \
  -e QT_QPA_PLATFORM=offscreen \
  -v "$PWD/output:/opt/brickr/output" \
  brickr:local \
  --cli \
  --input /opt/brickr/models/toyplane.obj \
  --resolution 30 \
  --print-stats \
  --export-obj /opt/brickr/output/toyplane.obj \
  --save-instructions /opt/brickr/output/toyplane.svg