修复保存浏览器数量列browser_count缺失报错

Co-Authored-By: Warp <agent@warp.dev>

src/core/database.py

@@ -512,6 +512,7 @@ class Database:
                     page_action TEXT DEFAULT 'FLOW_GENERATION',
                     browser_proxy_enabled BOOLEAN DEFAULT 0,
                     browser_proxy_url TEXT,
+                    browser_count INTEGER DEFAULT 1,
                     created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
                     updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
                 )