feat: 为应用版本查询增加appCode参数支持

新增应用版本类型的AppCode字段，修改相关接口和实现以支持通过appCode查询指定应用的最新版本，增加appCode合法性校验，完善缓存键以区分不同应用的版本信息

server/im_http.go

@@ -2287,10 +2287,18 @@ func serveIMAppReleaseLatest(wrt http.ResponseWriter, req *http.Request) {
 	}
 	platform := strings.ToLower(strings.TrimSpace(req.URL.Query().Get("platform")))
 	channel := strings.ToLower(strings.TrimSpace(req.URL.Query().Get("channel")))
+	appCode := strings.ToLower(strings.TrimSpace(req.URL.Query().Get("app_code")))
 	currentVersion := strings.TrimSpace(req.URL.Query().Get("current_version"))
 	if channel == "" {
 		channel = "stable"
 	}
+	if appCode == "" {
+		appCode = "im"
+	}
+	if !isValidAppCode(appCode) {
+		writeIMError(wrt, req, http.StatusBadRequest, 30000, imReasonMalformedRequest, "malformed request", map[string]any{"field": "app_code"})
+		return
+	}
 	if platform != "ios" && platform != "android" && platform != "web" {
 		writeIMError(wrt, req, http.StatusBadRequest, 30000, imReasonMalformedRequest, "malformed request", map[string]any{"field": "platform"})
 		return
@@ -2300,7 +2308,7 @@ func serveIMAppReleaseLatest(wrt http.ResponseWriter, req *http.Request) {
 		writeIMError(wrt, req, http.StatusBadRequest, 30000, imReasonMalformedRequest, "malformed request", map[string]any{"field": "current_version"})
 		return
 	}
-	release, err := store.AppReleases.Latest(platform, channel)
+	release, err := store.AppReleases.Latest(appCode, platform, channel)
 	if err != nil {
 		if platform == "web" {
 			logs.Warn.Println("im app release latest: using web fallback", err)
@@ -8782,6 +8790,19 @@ func appReleasePayload(release *types.AppRelease, currentVersion string, hasUpda
 	}
 }
 
+func isValidAppCode(raw string) bool {
+	if raw == "" || len(raw) > 32 {
+		return false
+	}
+	for _, r := range raw {
+		if (r >= 'a' && r <= 'z') || (r >= '0' && r <= '9') || r == '-' || r == '_' {
+			continue
+		}
+		return false
+	}
+	return true
+}
+
 func parseNumericAppVersion(raw string) ([]uint64, error) {
 	raw = strings.TrimPrefix(strings.ToLower(strings.TrimSpace(raw)), "v")
 	parts := strings.Split(raw, ".")