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>

config.example.toml

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+# artmap configuration
+
+[settings]
+listen_port = 6454              # ArtNet port (default: 6454)
+broadcast_addr = "2.255.255.255" # ArtNet broadcast address
+
+# Universe address formats supported:
+#   "0.0.1"  - Net.Subnet.Universe
+#   "0:0:1"  - Net:Subnet:Universe
+#   1        - Universe number only (net=0, subnet=0)
+#   "1"      - Universe number as string
+
+# Example: Remap entire universe
+# Maps all 512 channels from universe 0 to universe 5
+[[mapping]]
+from = "0.0.0"
+to = "0.0.5"
+
+# Example: Channel-level remap for fixture spillover
+# Maps channels 450-512 from universe 0 to channels 1-63 of universe 1
+# Use case: A fixture at the end of universe 0 spills into universe 1
+[[mapping]]
+from = "0.0.0"
+from_channel = 450    # 1-512 (1-indexed, like DMX)
+to = "0.0.1"
+to_channel = 1
+count = 63            # Number of channels to remap
+
+# Example: Using plain universe numbers
+[[mapping]]
+from = 2
+to = 10
+
+# Example: Multiple outputs from same source
+# The same source channels can be mapped to multiple destinations
+[[mapping]]
+from = "0.0.3"
+to = "0.0.7"
+
+[[mapping]]
+from = "0.0.3"
+to = "0.0.8"