Initial commit: DHCP whitelist service for direct link connections

Features:
- Docker-based DHCP server with MAC address whitelisting
- Binds to specific ethernet interface only
- NO DNS/gateway advertised (direct link only, not a router)
- Configurable network parameters (subnet, DHCP range, lease times)
- Systemd service integration for Arch/Manjaro
- Test environment with isolated network (172.20.0.0/24)
- Auto-configuration script to detect network settings
- Complete Makefile with management targets

Security:
- Only responds to whitelisted MAC addresses
- deny unknown-clients configuration
- Runs in Docker container for isolation

Configuration:
- Copy .example files to create your config
- interface.conf: Network interface to bind to
- whitelist.conf: Allowed MAC addresses
- network.conf: Network parameters (optional)

test/test-config/interface.conf

@@ -0,0 +1 @@
+eth0

test/test-config/network.conf

@@ -0,0 +1,20 @@
+# Network configuration for TEST DHCP server
+# Uses 172.20.0.0/24 to avoid conflicts with common networks
+
+# Network subnet (overrides auto-detection)
+SUBNET=172.20.0.0
+
+# Netmask in dotted notation
+NETMASK=255.255.255.0
+
+# DHCP range start offset from network base
+RANGE_START_OFFSET=10
+
+# DHCP range end offset from network base
+RANGE_END_OFFSET=100
+
+# Lease time in seconds (shorter for testing)
+LEASE_TIME=300
+
+# Max lease time in seconds
+MAX_LEASE_TIME=600

test/test-config/whitelist.conf

@@ -0,0 +1 @@
+02:42:ac:11:00:02