feat(app): migrate /app accounts to Vue SPA (stage 3)

app.py

@@ -1202,7 +1202,14 @@ def register_page():
 @login_required
 def app_page():
     """主应用页面"""
-    return render_template('index.html')
+    return render_app_spa_or_legacy('index.html')
+
+
+@app.route('/app/<path:subpath>')
+@login_required
+def app_page_subpath(subpath):
+    """SPA 子路由刷新支持（History 模式）"""
+    return render_app_spa_or_legacy('index.html')
 
 
 @app.route('/yuyx')
@@ -2608,6 +2615,33 @@ def delete_account(account_id):
     return jsonify({"success": True})
 
 
+@app.route('/api/accounts/clear', methods=['POST'])
+@login_required
+def clear_accounts():
+    """清空当前用户的所有账号"""
+    user_id = current_user.id
+
+    accounts = user_accounts.get(user_id, {})
+    if any(acc.is_running for acc in accounts.values()):
+        return jsonify({"error": "有任务正在运行，请先停止后再清空"}), 400
+
+    account_ids = list(accounts.keys())
+
+    deleted = database.delete_user_accounts(user_id)
+
+    # 清理内存缓存
+    if user_id in user_accounts:
+        user_accounts[user_id] = {}
+
+    # 清理任务状态缓存
+    for account_id in account_ids:
+        safe_remove_task_status(account_id)
+        safe_remove_task(account_id)
+
+    log_to_client(f"清空账号: {deleted} 个", user_id)
+    return jsonify({"success": True, "deleted": deleted})
+
+
 @app.route('/api/accounts/<account_id>/remark', methods=['PUT'])
 @login_required
 def update_remark(account_id):
@@ -3380,6 +3414,10 @@ def take_screenshot_for_account(user_id, account_id, browse_type="应读", sourc
     )
     if not submitted:
         screenshot_callback(None, "截图队列已满，请稍后重试")
+
+
+@app.route('/api/accounts/<account_id>/screenshot', methods=['POST'])
+@login_required
 def manual_screenshot(account_id):
     """手动为指定账号截图"""
     user_id = current_user.id