Add Coolify deployment support

Multi-stage Dockerfile builds the email-builder, admin frontend, and Go
backend from source and stuffs assets into the binary. The runtime-only
image moved to Dockerfile.goreleaser for release builds. Adds a Coolify
compose file with magic service variables, healthchecks, and volumes.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docker-compose.coolify.yml

@@ -0,0 +1,68 @@
+# Coolify deployment for EagleCast.
+#
+# In Coolify: create a new resource -> Docker Compose -> point it at this
+# repository and set "Docker Compose Location" to /docker-compose.coolify.yml.
+# Coolify substitutes the $SERVICE_* magic variables below: it generates the
+# database password automatically and assigns the public domain (FQDN) you
+# configure to the eaglecast service on port 9000. TLS and the reverse proxy
+# are handled by Coolify's own proxy, so no ports are published here.
+#
+# Optional: set EAGLECAST_ADMIN_USER / EAGLECAST_ADMIN_PASSWORD in the
+# Coolify environment variables UI before the first deploy to auto-create the
+# Super Admin. Otherwise, visit the app after deploy to create it.
+#
+# After the first login, set the root URL in Admin -> Settings -> General to
+# your public https:// domain so links in e-mails point at the right host.
+
+services:
+  eaglecast:
+    build:
+      context: .
+      dockerfile: Dockerfile
+    restart: unless-stopped
+    environment:
+      - SERVICE_FQDN_EAGLECAST_9000
+      - EAGLECAST_app__address=0.0.0.0:9000
+      - EAGLECAST_db__host=db
+      - EAGLECAST_db__port=5432
+      - EAGLECAST_db__user=eaglecast
+      - EAGLECAST_db__password=$SERVICE_PASSWORD_EAGLECASTDB
+      - EAGLECAST_db__database=eaglecast
+      - EAGLECAST_db__ssl_mode=disable
+      - EAGLECAST_db__max_open=25
+      - EAGLECAST_db__max_idle=25
+      - EAGLECAST_db__max_lifetime=300s
+      - TZ=Etc/UTC
+      - EAGLECAST_ADMIN_USER=${EAGLECAST_ADMIN_USER:-}
+      - EAGLECAST_ADMIN_PASSWORD=${EAGLECAST_ADMIN_PASSWORD:-}
+    command: [sh, -c, "./eaglecast --install --idempotent --yes --config '' && ./eaglecast --upgrade --yes --config '' && ./eaglecast --config ''"]
+    depends_on:
+      db:
+        condition: service_healthy
+    volumes:
+      - eaglecast-uploads:/eaglecast/uploads
+    healthcheck:
+      test: ["CMD", "wget", "-qO-", "http://127.0.0.1:9000/health"]
+      interval: 30s
+      timeout: 5s
+      retries: 5
+      start_period: 30s
+
+  db:
+    image: postgres:17-alpine
+    restart: unless-stopped
+    environment:
+      - POSTGRES_USER=eaglecast
+      - POSTGRES_PASSWORD=$SERVICE_PASSWORD_EAGLECASTDB
+      - POSTGRES_DB=eaglecast
+    volumes:
+      - eaglecast-data:/var/lib/postgresql/data
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U eaglecast"]
+      interval: 10s
+      timeout: 5s
+      retries: 6
+
+volumes:
+  eaglecast-data:
+  eaglecast-uploads: