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)

docker-compose.test.yml

@@ -0,0 +1,45 @@
+version: '3.8'
+
+networks:
+  test-net:
+    driver: bridge
+    ipam:
+      config:
+        - subnet: 172.20.0.0/24
+          gateway: 172.20.0.1
+
+services:
+  test-dhcp-server:
+    build: .
+    image: dhcp-whitelist:test
+    container_name: test-dhcp-server
+    networks:
+      test-net:
+        ipv4_address: 172.20.0.2
+    volumes:
+      - ./test/test-config:/config:ro
+    environment:
+      - TZ=UTC
+    cap_add:
+      - NET_ADMIN
+      - NET_RAW
+
+  test-client-allowed:
+    build: ./test/test-client
+    container_name: test-client-allowed
+    networks:
+      test-net:
+    mac_address: "02:42:ac:11:00:02"
+    depends_on:
+      - test-dhcp-server
+    command: ["/bin/sh", "-c", "sleep 5 && udhcpc -i eth0 -n -q && ip addr show eth0"]
+
+  test-client-denied:
+    build: ./test/test-client
+    container_name: test-client-denied
+    networks:
+      test-net:
+    mac_address: "02:42:ac:11:00:99"
+    depends_on:
+      - test-dhcp-server
+    command: ["/bin/sh", "-c", "sleep 5 && timeout 10 udhcpc -i eth0 -n -q || echo 'DHCP request denied as expected'"]