Release v0.3.1-alpha

Added: project-level dmx.toml universe → device mapping.

See Changes.md for details. Highlights:
- <project>/dmx.toml encodes which DMX adapter drives which universe
- 'serial:<USB_SERIAL>' resolves to a stable /dev/serial/by-id path
- Two-pass resolution prevents auto-detect from stealing explicit bindings
- --print-dmx-resolution CLI flag for verifying wiring
- Workspace 0.3.0-rc2 -> 0.3.1-alpha