build: create a reproducible Void Linux contributor environment

[amandeavor]

Goal

Give contributors one documented, reproducible Void Linux environment for checking components without modifying their main system.

Scope

Create either a container definition or a tightly documented disposable VM workflow that can:

• install pinned or recorded build dependencies
• run the current Rust formatting and check commands
• build VelocityMind with strict warnings
• prepare the GTK/Tauri dependencies incrementally
• avoid mounting or exposing real block devices by default

Acceptance criteria

• a fresh contributor can follow the instructions from a clean host
• versions and architecture are visible in logs
• no signing keys or privileged host paths are required for basic checks
• CI and local commands share the same entry points where practical
• known unsupported components are reported clearly

This is an ownership-sized project and a good path toward maintaining build and release infrastructure.