Fix Docker registry timeout by using pinned Node.js version

- Switch to node:18.19.0-alpine for better registry availability
- Pinned versions are more reliably cached by Docker registries
- Should resolve Railway deployment timeout issues

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Author: alanops

Dockerfile

@@ -1,5 +1,5 @@
-# Ultra-minimal build for Railway
-FROM node:18-alpine
+# Ultra-minimal build for Railway - pinned version for reliability
+FROM node:18.19.0-alpine
 
 WORKDIR /app