feat: 修复 H5 底部导航覆盖 + 更新项目进度文档

## H5 底部导航修复 (Bug #10)
- 精简 App.vue，移除重复 tabbar，仅保留全局样式
- uni-page 设置 height: calc(100% - 50px) + overflow-y: auto
- 内容区域精确停在底部导航上方，独立滚动不再叠加
- 恢复 custom-tab-bar 组件

## 项目进度文档
- PROGRESS.md 更新至 10 个 Bug 修复
- 新增 H5 底部导航修复记录
- 新增历史变更条目

backend/app/services/export.py

@@ -0,0 +1,37 @@
+from typing import List, Dict, Any
+import csv
+import io
+
+
+def export_customers_csv(customers: List[Dict[str, Any]]) -> bytes:
+    output = io.StringIO()
+    writer = csv.writer(output)
+    writer.writerow(["Name", "Company", "Country", "Phone", "Email", "Status", "Last Contact"])
+    for c in customers:
+        writer.writerow([
+            c.get("name", ""),
+            c.get("company", ""),
+            c.get("country", ""),
+            c.get("phone", ""),
+            c.get("email", ""),
+            c.get("status", ""),
+            c.get("last_contact_at", ""),
+        ])
+    return output.getvalue().encode("utf-8-sig")
+
+
+def export_quotations_csv(quotations: List[Dict[str, Any]]) -> bytes:
+    output = io.StringIO()
+    writer = csv.writer(output)
+    writer.writerow(["Title", "Customer", "Currency", "Subtotal", "Total", "Status", "Date"])
+    for q in quotations:
+        writer.writerow([
+            q.get("title", ""),
+            q.get("customer_name", ""),
+            q.get("currency", "USD"),
+            q.get("subtotal", 0),
+            q.get("total", 0),
+            q.get("status", ""),
+            q.get("created_at", ""),
+        ])
+    return output.getvalue().encode("utf-8-sig")