Add Docker production build and update README

- Multi-stage Dockerfile: builds frontend, packages with Python backend
- admin.py serves frontend/dist as StaticFiles in production
- docker-entrypoint.sh runs proxy + admin-api, exits cleanly if either dies
- .dockerignore excludes .env, venv, tests, node_modules
- Split requirements.txt (prod) / requirements-dev.txt (dev+test)
- aiofiles added for StaticFiles support
- start.sh: port checks before startup, venv auto-activation, trap cleanup
- vite.config.js: clearScreen disabled
- README rewritten to reflect current architecture

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.dockerignore

@@ -0,0 +1,11 @@
+.git/
+.venv/
+venv/
+.env
+frontend/node_modules/
+frontend/dist/
+backend/__pycache__/
+backend/**/__pycache__/
+backend/*.pyc
+backend/test.db
+backend/tests/