feat: add Docker support and compile shared package to dist

- Add multi-stage Dockerfile for server containerization
- Add .dockerignore to exclude unnecessary files from build context
- Switch shared package from source to compiled CommonJS output (dist/)
- Server dev/build scripts now build shared package first
- Fix deep imports to use @calchat/shared barrel export
- Update CLAUDE.md with Docker and shared package documentation

packages/shared/.gitignore

@@ -0,0 +1 @@
+dist/