feat: initial project structure

- Add FastAPI app with paper browsing UI and REST API
- Add crawler service and database models
- Add scripts for DB init and manual crawl
- Add docs (api-and-ui, data-model, services)
- Add requirements and project config

.gitignore

@@ -0,0 +1,15 @@
+.env
+__pycache__/
+*.pyc
+*.pyo
+data/db/*.db
+data/papers/
+data/tmp/
+data/chroma/
+logs/*.log
+.venv/
+venv/
+*.egg-info/
+dist/
+build/
+.DS_Store