refactor: 彻底消除硬编码 qq — 平台标识统一为 obv11

- PlatformName() 返回 "obv11"
- platformFormats key: "obv11"
- 所有 platform == "qq" 检查 → "obv11"
- session prefix: platform_qq_ → platform_obv11_
- env var PLATFORM_CHANNELS: obv11:group:xxx
- ethend 平台标识同步更新
- 注释和测试用例同步

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

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

@@ -33,7 +33,7 @@ type PendingThought struct {
 // ProactiveTarget describes the target for proactive platform messages (OBv11, etc.).
 // When nil, the message goes through the existing Web push path.
 type ProactiveTarget struct {
-	Platform string // "qq"
+	Platform string // "obv11"
 	ChatType string // "private" or "group"
 	UserID   string // OBv11 user number
 	GroupID  string // OBv11 group number (group chat)
@@ -71,7 +71,7 @@ type PlatformFormat struct {
 // defaultPlatformFormats returns the built-in platform format registry.
 func defaultPlatformFormats() map[string]*PlatformFormat {
 	formats := make(map[string]*PlatformFormat)
-	qq := &PlatformFormat{
+	obv11 := &PlatformFormat{
 		Label:            "OBv11",
 		TargetRegex:      `【OBv11(私聊|群聊):(\d+)(?:@(\d+))?】`,
 		GroupMarkerFmt:   "【OBv11群聊:%s】",
@@ -80,14 +80,14 @@ func defaultPlatformFormats() map[string]*PlatformFormat {
 		GroupKeyword:     "群聊",
 		PrivateKeyword:   "私聊",
 	}
-	qq.compiled = regexp.MustCompile(qq.TargetRegex)
-	formats["qq"] = qq
+	obv11.compiled = regexp.MustCompile(obv11.TargetRegex)
+	formats["obv11"] = obv11
 	return formats
 }
 
 // ParsePlatformChannels parses PLATFORM_CHANNELS env var.
-// Format: "qq:group:123456,telegram:group:789012"
-// Optional 4th field for display name: "qq:group:123456:群名称"
+// Format: "obv11:group:123456,telegram:group:789012"
+// Optional 4th field for display name: "obv11:group:123456:群名称"
 func ParsePlatformChannels(raw string) []PlatformChannel {
 	if raw == "" {
 		return nil
@@ -228,7 +228,7 @@ type Thinker struct {
 	platformChannels      []PlatformChannel
 	platformThinkInterval time.Duration
 
-	// 平台 Bot UID (platform -> bot's own UID, e.g. "qq" -> "123456789")
+	// 平台 Bot UID (platform -> bot's own UID, e.g. "obv11" -> "123456789")
 	botUIDs map[string]string
 
 	// 平台格式注册表 (platform -> format)
@@ -1609,15 +1609,15 @@ func (t *Thinker) buildThinkingUserPrompt(
 			sb.WriteString("\n\n【你的平台身份与可用频道】\n")
 
 			// Bot's own identity.
-			if qqBotUID, ok := botUIDs["qq"]; ok && qqBotUID != "" {
+			if qqBotUID, ok := botUIDs["obv11"]; ok && qqBotUID != "" {
 				sb.WriteString(fmt.Sprintf("你在OBv11上的账号是: %s（昔涟），这就是你。\n", qqBotUID))
 			}
 
 			// Active session context with time, group name, and trigger-aware guidance.
-			if strings.HasPrefix(activeSID, "platform_qq_") {
-				activeChID := strings.TrimPrefix(activeSID, "platform_qq_")
+			if strings.HasPrefix(activeSID, "platform_obv11_") {
+				activeChID := strings.TrimPrefix(activeSID, "platform_obv11_")
 				for _, ch := range qqChannels {
-					if ch.Platform == "qq" && ch.ChannelID == activeChID {
+					if ch.Platform == "obv11" && ch.ChannelID == activeChID {
 						chLabel := activeChID
 						if ch.ChannelName != "" {
 							chLabel = fmt.Sprintf("%s(%s)", ch.ChannelName, activeChID)
@@ -1665,7 +1665,7 @@ func (t *Thinker) buildThinkingUserPrompt(
 			sb.WriteString("- OBv11群聊@某人: 【主动消息】【OBv11群聊:群号@账号】消息内容\n")
 			sb.WriteString("\n可用的平台频道列表：\n")
 			for _, ch := range qqChannels {
-				if ch.Platform != "qq" {
+				if ch.Platform != "obv11" {
 					continue
 				}
 				label := ch.ChannelID