refactor: 平台改为代码内置 provider 架构，一次性迁移现有数据 - 新增 app/providers：BalanceProvider 基类 + DeepSeek 适配器 + 注册表 - platforms 表去除 method/url/headers/body/balance_path，新增 provider_id - 现有数据库已一次性迁移（备份 data/monitor.db.bak-v1），不保留迁移工具 - 平台 UI 改为选择内置提供方；fetcher/monitor 走 provider 构建请求与解析 - 表达式引擎（运算符/函数）随架构保留，供 provider 内部使用 - 测试更新至 provider 模式，共 92 个

tests/test_monitor.py

@@ -12,8 +12,7 @@ def _row(**overrides):
         "threshold": 0, "enabled": 1, "alert_armed": 1,
         "last_balance": None, "last_status": "pending", "last_error": "",
         "last_check_at": None, "note": "",
-        "platform_name": "P", "currency": "USD", "icon": "", "method": "GET",
-        "url": "http://x", "headers": "{}", "body": "", "balance_path": "b",
+        "provider_id": "deepseek", "platform_name": "P", "currency": "USD", "icon": "",
         "interval_seconds": None, "retry_count": None, "timeout_seconds": None,
         "platform_enabled": 1, "platform_note": "",
     }
@@ -32,8 +31,8 @@ class TestSplit:
         assert platform["name"] == "P"
         assert platform["id"] == 2
         assert platform["enabled"] == 1
-        assert platform["url"] == "http://x"
-        assert platform["balance_path"] == "b"
+        assert platform["provider_id"] == "deepseek"
+        assert platform["currency"] == "USD"
 
     def test_plain_key_passthrough(self):
         """未编码的 key（历史数据）原样使用，不抛错。"""