feat: 同平台多账号支持 — adapter_name 贯穿全链路

- UnifiedMessage 新增 AdapterName 字段
- router 从适配器 ConfigName() 捕获 adapter 实例名
- forwardToAICore source 新增 adapter_name
- ai-core SetBotUID key 优先用 adapter_name，回退 platform
- 更新优化大纲加入 P4.1

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

backend/platform-bridge/cmd/main.go

@@ -665,6 +665,7 @@ func forwardToAICore(cfg *config.Config, msg *bridge.UnifiedMessage, mode, userI
 			"original_uid":  msg.OriginalSenderUID,
 			"bot_uid":       msg.BotUID,
 			"group_name":    msg.GroupName,
+			"adapter_name":  msg.AdapterName,
 		},
 	}
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