chore: update gitignore and add config files

- Add frontend/dist and backend/dist to gitignore
- Remove build artifacts from tracking
- Add .dockerignore and .env.example

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

.dockerignore

@@ -0,0 +1,15 @@
+node_modules
+dist
+.git
+.gitignore
+*.md
+.env
+.env.*
+!.env.example
+*.log
+.DS_Store
+frontend/node_modules
+frontend/dist
+backend/node_modules
+backend/dist
+backend/prisma/data