Initial implementation of ArtNet remapping proxy

Channel-level DMX remapping between ArtNet universes with:
- TOML configuration with multiple address formats (net.subnet.universe, plain number)
- ArtPoll discovery for output nodes
- Configurable channel ranges for fixture spillover handling

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

go.mod

@@ -0,0 +1,5 @@
+module github.com/gopatchy/artmap
+
+go 1.25.4
+
+require github.com/BurntSushi/toml v1.6.0