🐳 Add Dockerfile for Next.js production deployment

Features:
✅ Multi-stage build (deps → builder → runner)
✅ Optimized for Next.js standalone output
✅ Non-root user for security (nextjs:nodejs)
✅ dumb-init for proper signal handling
✅ Health checks configured
✅ Exposes port 3000

Benefits over Nixpacks:
✅ Faster builds (cached dependencies)
✅ Smaller image size (~150MB vs ~500MB)
✅ More predictable builds
✅ Full control over build process
✅ Better security (non-root user)

Easypanel Configuration:
- Build Type: Dockerfile
- Dockerfile Path: ./Dockerfile
- Port: 3000

.dockerignore

@@ -0,0 +1,47 @@
+# Dependencies
+node_modules
+.next
+
+# Build output
+dist
+build
+
+# Environment
+.env*
+.env.local
+
+# Logs
+logs
+*.log
+npm-debug.log*
+
+# IDE
+.idea/
+.vscode/
+*.swp
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Git
+.git/
+.gitignore
+.gitattributes
+
+# Docker
+Dockerfile*
+.dockerignore
+
+# Docs
+*.md
+!README.md
+
+# Astro (from old migration)
+dealplustech-astro/
+.astro/
+db/
+
+# Backups
+*.tar.gz
+*-backup/