fix: safe type assertions across OAuth, model Scan, relay, and middleware

- OAuth: safe type assertions for session state and affiliate code
  (oauth.go, github.go, discord.go, linuxdo.go, oidc.go)
- Model: Scan() methods handle string values from DB drivers, not just []byte
  (channel.go ChannelInfo, task.go Properties/TaskPrivateData)
- Model: safe type assertion in CleanupChannelPollingLocks sync.Map iteration
- Relay: safe type assertions in audio_handler, AWS InvokeModel,
  ollama ConvertClaudeRequest, claude stop sequences, zhipu token cache
- Service: fix slice bounds panic in Gemini->OpenAI stop sequences conversion
- Service: safe type assertion in CleanupFileSources middleware
- Middleware: add missing c.Abort() in turnstile session save failure
- Middleware: safe type assertion in distributor channelId
- Middleware: safe int comparison in auth helper

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

heicode/middleware/auth.go

@@ -112,7 +112,8 @@ func authHelper(c *gin.Context, minRole int) {
 		return
 
 	}
-	if id != apiUserId {
+	idVal, _ := id.(int)
+	if idVal != apiUserId {
 		c.JSON(http.StatusUnauthorized, gin.H{
 			"success": false,
 			"message": common.TranslateMessage(c, i18n.MsgAuthUserIdMismatch),