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

app/templates/index.html

@@ -0,0 +1,36 @@
+{% extends "base.html" %}
+
+{% block title %}{{ page_title }} — HF Daily Papers{% endblock %}
+
+{% block content %}
+<div class="date-nav">
+  {% if prev_day %}
+  <a href="/day/{{ prev_day }}" class="date-nav-btn">← 前一天</a>
+  {% endif %}
+  <h1 class="date-title">{{ current_date }}</h1>
+  {% if next_day <= today %}
+  <a href="/day/{{ next_day }}" class="date-nav-btn">后一天 →</a>
+  {% endif %}
+  <a href="/day/{{ today }}" class="date-nav-btn">今日</a>
+</div>
+
+{% if papers %}
+<div class="paper-list">
+  {% for paper in papers %}
+  {% include "partials/paper_card.html" %}
+  {% endfor %}
+</div>
+{% else %}
+<div class="empty-state">
+  <p>📭 当天暂无论文数据</p>
+  <p class="hint">试试浏览其他日期，或使用管理接口抓取数据</p>
+</div>
+{% endif %}
+
+<div class="date-quick-nav">
+  <span>有数据的日期：</span>
+  {% for d in available_dates[:10] %}
+  <a href="/day/{{ d }}" class="date-chip {% if d == current_date %}active{% endif %}">{{ d }}</a>
+  {% endfor %}
+</div>
+{% endblock %}