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>

Dockerfile.goreleaser

@@ -0,0 +1,26 @@
+FROM alpine:latest
+
+# Install dependencies
+RUN apk --no-cache add ca-certificates tzdata shadow su-exec
+
+# Set the working directory
+WORKDIR /eaglecast
+
+# Copy only the necessary files
+COPY eaglecast .
+COPY config.toml.sample config.toml
+
+# Copy the entrypoint script
+COPY docker-entrypoint.sh /usr/local/bin/
+
+# Make the entrypoint script executable
+RUN chmod +x /usr/local/bin/docker-entrypoint.sh
+
+# Expose the application port
+EXPOSE 9000
+
+# Set the entrypoint
+ENTRYPOINT ["docker-entrypoint.sh"]
+
+# Define the command to run the application
+CMD ["./eaglecast"]