Simplify Docker setup across desktop and homelab

[Bromeego]

What changed

• use stable Docker-managed volumes by default with no required .env file
• discover named-volume or bind-folder mounts automatically for each SimulationCraft job
• add an optional homelab bind-folder Compose overlay
• add Windows and macOS/Linux launchers
• add a desktop and homelab setup guide
• validate every Compose and local-build combination in CI

Why

The original deployment required users to calculate and repeat absolute host paths so the web container could launch SimulationCraft. Docker already knows the resolved mount sources, so the app can reuse those directly. This makes personal setup much simpler while retaining explicit host-folder storage for homelabs.

Validation

• 20 Python tests with the project virtual environment
• 20 Python tests inside the built Python 3.12 image
• JavaScript interface test
• four Compose configuration combinations
• Docker image build
• direct official SimulationCraft smoke test
• real web simulation with named volumes
• real web simulation with homelab bind folders
• launcher startup and health wait
• clean whitespace validation

Release plan

Publish v0.3.0-rc.1 from this branch for Windows and homelab testing before merging and promoting v0.3.0.