fix: reminder platform 改用 AdapterName（唯一标识符），不再硬编码 obv11

- ProcessParams/SynthesizeParams 新增 AdapterName
- main.go 传递 req.Source.AdapterName
- reminder_create 自动注入使用 adapter 名而非平台类型

Co-Authored-By: Claude <noreply@anthropic.com>

backend/ai-core/cmd/main.go

@@ -1086,6 +1086,7 @@ func handleChat(
 		ChannelType: req.Source.ChannelType,
 		ChannelID:   req.Source.ChannelID,
 		BotUID:      req.Source.BotUID,
+		AdapterName: req.Source.AdapterName,
 	})
 	if err != nil {
 		fallback := getFallbackMessage()