Initial commit: AIS vessel position tracking microservice

Go service that connects to aisstream.io websocket, filtered by MMSIs
from track_devices table. Writes positions to aisstream_pos (24h TTL)
and upserts latest position per vessel to aisstream_last. Reloads
MMSI list every 5 minutes to pick up changes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -0,0 +1,18 @@
+services:
+  aisstream:
+    build: .
+    container_name: aisstream
+    environment:
+      POSTGRES_HOST: ${POSTGRES_HOST}
+      POSTGRES_DB: ${POSTGRES_DB}
+      POSTGRES_USER: ${POSTGRES_USER}
+      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD}
+      POSTGRES_PORT: ${POSTGRES_PORT}
+      AISSTREAM_API_KEY: ${AISSTREAM_API_KEY}
+    networks:
+      - postgres_network
+    restart: unless-stopped
+
+networks:
+  postgres_network:
+    external: true