Initial commit: Shlink docker compose stack

Self-hosted Shlink URL shortener with the official web dashboard,
backed by PostgreSQL 16. Designed to sit behind a reverse proxy
that terminates TLS.

- shlink server exposed on host port 8500
- shlink-web-client dashboard exposed on host port 8501
- postgres 16 kept internal, persisted via named volume
- dashboard preconfigured via SHLINK_PUBLIC_URL + INITIAL_API_KEY
- .env.example documents required variables; .env is gitignored

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.env.example

@@ -0,0 +1,27 @@
+# Domain used to build short URLs (no scheme)
+DEFAULT_DOMAIN=s.example.com
+
+# Set to false if your reverse proxy does NOT terminate TLS
+IS_HTTPS_ENABLED=true
+
+# Public URL the dashboard uses to reach the Shlink API (with scheme)
+SHLINK_PUBLIC_URL=https://s.example.com
+
+# Initial API key created on first boot — also used to preconfigure the dashboard
+# Generate with: openssl rand -hex 32
+INITIAL_API_KEY=change-me-to-a-long-random-string
+
+# Optional MaxMind GeoLite2 license key for IP geolocation
+GEOLITE_LICENSE_KEY=
+
+# Timezone
+TIMEZONE=UTC
+
+# Postgres
+POSTGRES_DB=shlink
+POSTGRES_USER=shlink
+POSTGRES_PASSWORD=change-me
+
+# Host ports exposed to the reverse proxy
+SHLINK_SERVER_PORT=8500
+SHLINK_DASHBOARD_PORT=8501