Refactor DDNS updater: switch to Alpine, support multiple domains

- Replace golang base image with alpine for smaller footprint
- Add bash/curl dependencies explicitly
- Refactor script to support multiple domains via arrays
- Improve logging with timestamps and status messages
- Simplify docker-compose configuration
- Remove obsolete build scripts and env files

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

docker-compose.yml

@@ -0,0 +1,11 @@
+services:
+  ddns:
+    build: .
+    container_name: ddns
+    restart: unless-stopped
+    networks:
+      - proxy
+
+networks:
+  proxy:
+    external: true