Refactor config format and improve consistency

Config changes:
- Use protocol prefixes in addresses: "sacn:64:361-450" -> "artnet:0.0.0:1"
- Remove separate from_proto/proto fields
- Targets now include protocol: universe = "artnet:0.0.0"

CLI changes:
- Rename --listen to --artnet-listen (empty to disable)
- Fix --debug help text

Logging changes:
- Use [<-proto] and [->proto] prefixes for direction
- Consistent lowercase key=value format
- Refactor duplicate send code into sendOutputs()

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

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

config.example.toml

@@ -1,77 +1,68 @@
 # artmap configuration
-# Run with: go run . -config config.toml [-listen :6454]
+# Run with: go run . -config config.toml [-artnet-listen :6454]
 
 # Target addresses for ArtNet output universes
-# Configure the destination IP (broadcast or unicast) for each output universe
+# Each output universe needs a target IP (broadcast or unicast)
 # ArtPoll discovery will be sent to all unique target addresses
 [[target]]
-universe = "0.0.0"
+universe = "artnet:0.0.0"
 address = "2.255.255.255"
 
 [[target]]
-universe = "0.0.5"
+universe = "artnet:0.0.5"
 address = "10.50.255.255"
 
 # Address format:
-#   from: universe[:channels]  - range specifies which channels to read
-#   to:   universe[:channel]   - single channel specifies where to start writing
+#   proto:universe[:channels]
+#
+# Protocol prefix (required):
+#   artnet: - ArtNet protocol
+#   sacn:   - sACN/E1.31 protocol
 #
 # Universe: "net.subnet.universe" or plain number (all 0-indexed, 0-127.0-15.0-15)
 # Channels: 1-indexed (1-512), matching DMX convention
 #
 # From examples:
-#   "0.0.1"        - universe 1, all channels (1-512)
-#   "0.0.1:50"     - universe 1, channel 50 only
-#   "0.0.1:50-"    - universe 1, channels 50-512
-#   "0.0.1:50-100" - universe 1, channels 50-100
-#   1              - universe 1, all channels
-#   "1:50-100"     - universe 1, channels 50-100
+#   "artnet:0.0.1"        - universe 1, all channels (1-512)
+#   "sacn:64:50"          - universe 64, channel 50 only
+#   "artnet:0.0.1:50-"    - universe 1, channels 50-512
+#   "sacn:1:50-100"       - universe 1, channels 50-100
 #
 # To examples:
-#   "0.0.1"        - universe 1, starting at channel 1
-#   "0.0.1:50"     - universe 1, starting at channel 50
-#
-# Input protocol (optional, default "artnet"):
-#   from_proto = "artnet"  - receive via ArtNet
-#   from_proto = "sacn"    - receive via sACN/E1.31 (multicast)
-#
-# Output protocol (optional, default "artnet"):
-#   proto = "artnet"  - output via ArtNet (broadcast or discovered nodes)
-#   proto = "sacn"    - output via sACN/E1.31 (multicast)
+#   "artnet:0.0.1"        - universe 1, starting at channel 1
+#   "sacn:1:50"           - universe 1, starting at channel 50
 
 # Remap entire universe
 [[mapping]]
-from = "0.0.0"
-to = "0.0.5"
+from = "artnet:0.0.0"
+to = "artnet:0.0.5"
 
 # Channel-level remap for fixture spillover
 # Channels 450-512 from universe 0 -> channels 1-63 of universe 1
 [[mapping]]
-from = "0.0.0:450-512"
-to = "0.0.1:1"
+from = "artnet:0.0.0:450-512"
+to = "artnet:0.0.1:1"
 
 # Using plain universe numbers
 [[mapping]]
-from = 2
-to = 10
+from = "artnet:2"
+to = "artnet:10"
 
 # Multiple outputs from same source
 [[mapping]]
-from = "0.0.3"
-to = "0.0.7"
+from = "artnet:0.0.3"
+to = "artnet:0.0.7"
 
 [[mapping]]
-from = "0.0.3"
-to = "0.0.8"
+from = "artnet:0.0.3"
+to = "artnet:0.0.8"
 
 # Output to sACN instead of ArtNet
 [[mapping]]
-from = "0.0.4"
-to = 1
-proto = "sacn"
+from = "artnet:0.0.4"
+to = "sacn:1"
 
 # Convert sACN input to ArtNet output
 [[mapping]]
-from = 5
-from_proto = "sacn"
-to = "0.0.5"
+from = "sacn:5"
+to = "artnet:0.0.5"