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

.env.example

@@ -0,0 +1,41 @@
+# ─── 应用 ────────────────────────────────
+APP_HOST=127.0.0.1
+APP_PORT=8000
+APP_DEBUG=false
+BASE_URL=http://127.0.0.1:8000
+APP_TIMEZONE=Asia/Shanghai
+
+# ─── 安全 ────────────────────────────────
+ADMIN_TOKEN=change-me
+
+# ─── HuggingFace / arXiv ────────────────
+HF_API_BASE=https://huggingface.co/api
+HF_PROXY=
+TOP_N=20
+HTTP_TIMEOUT_SECONDS=30
+HTTP_MAX_RETRIES=3
+HTTP_USER_AGENT=hf-daily-papers-local/0.1
+
+# ─── AI 总结（Phase 2 使用）──────────────
+PI_BIN=/home/rainbus/.local/share/mise/installs/pi/latest/pi
+SUMMARY_SKILL=daily-paper-summary
+SUMMARY_CONCURRENCY=3
+SUMMARY_TIMEOUT_SECONDS=300
+SUMMARY_MAX_RETRIES=1
+
+# ─── 调度（Phase 4 使用）─────────────────
+SCHEDULER_ENABLED=false
+SCHEDULE_HOUR=8
+SCHEDULE_MINUTE=0
+APP_WORKERS=1
+
+# ─── 数据库 ─────────────────────────────
+DATABASE_URL=sqlite:///data/db/papers.db
+
+# ─── 语义搜索（Phase 5 增强，暂留空）─────
+CHROMA_ENABLED=false
+CHROMA_DIR=data/chroma
+EMBED_API_BASE=
+EMBED_API_KEY=
+EMBED_MODEL=
+EMBED_DIMENSIONS=