fix: 私聊主动消息路由修复 + 多账号自动适配

- 正则兼容 private_ 前缀: 【OBv11私聊:private_1487720750】
- prompt 显示频道时自动剥离 private_ 前缀
- extractProactiveMessage 自动查 PlatformChannel 表，
  将 target.Platform 从格式key改为adapter实例名
  多账号场景下自动路由到正确adapter

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

backend/ai-core/internal/background/thinker.go

@@ -73,7 +73,7 @@ func defaultPlatformFormats() map[string]*PlatformFormat {
 	formats := make(map[string]*PlatformFormat)
 	obv11 := &PlatformFormat{
 		Label:            "OBv11",
-		TargetRegex:      `【OBv11(私聊|群聊):(\d+)(?:@(\d+))?】`,
+		TargetRegex:      `【OBv11(私聊|群聊):(?:private_)?(\d+)(?:@(\d+))?】`,
 		GroupMarkerFmt:   "【OBv11群聊:%s】",
 		PrivateMarkerFmt: "【OBv11私聊:%s】",
 		GroupAtMarkerFmt: "【OBv11群聊:%s@%s】",
@@ -1619,8 +1619,11 @@ func (t *Thinker) buildThinkingUserPrompt(
 				for _, ch := range qqChannels {
 					if ch.Platform == "obv11" && ch.ChannelID == activeChID {
 						chLabel := activeChID
+						displayChID := strings.TrimPrefix(activeChID, "private_")
 						if ch.ChannelName != "" {
-							chLabel = fmt.Sprintf("%s(%s)", ch.ChannelName, activeChID)
+							chLabel = fmt.Sprintf("%s(%s)", ch.ChannelName, displayChID)
+						} else if displayChID != activeChID {
+							chLabel = displayChID
 						}
 						// Last message time hint.
 						timeHint := ""
@@ -1885,8 +1888,25 @@ func (t *Thinker) extractProactiveMessage(content string) (string, *ProactiveTar
 					if m[1] == pf.GroupKeyword {
 						chatType = "group"
 					}
+					// Resolve adapter name from registered channels.
+					channelID := m[2]
+					if chatType == "private" {
+						channelID = "private_" + m[2]
+					}
+					adapterName := platform // fallback to format key
+					t.mu.Lock()
+					for _, ch := range t.platformChannels {
+						if ch.Platform == platform && ch.ChannelType == chatType && ch.ChannelID == channelID {
+							if ch.AdapterName != "" {
+								adapterName = ch.AdapterName
+							}
+							break
+						}
+					}
+					t.mu.Unlock()
+
 					target = &ProactiveTarget{
-						Platform: platform,
+						Platform: adapterName,
 						ChatType: chatType,
 						UserID:   m[2],
 						GroupID:  m[2],