fix: normalize input_text content blocks in Claude-to-OpenAI conversion

Clients like OpenClaw send input_text content blocks (a Responses API
type) through /v1/messages. The Claude-to-OpenAI converter silently
drops unknown types, so the message arrives empty at the upstream,
causing "Invalid value: 'input_text'" errors.

Map input_text to text since they share the same structure.

service/convert.go

@@ -127,7 +127,7 @@ func ClaudeToOpenAIRequest(claudeRequest dto.ClaudeRequest, info *relaycommon.Re
 
 			for _, mediaMsg := range contents {
 				switch mediaMsg.Type {
-				case "text":
+				case "text", "input_text":
 					message := dto.MediaContent{
 						Type:         "text",
 						Text:         mediaMsg.GetText(),