feat: show model name below conversion result

Add muted 'Responded by {model}' line below the output text so the
user knows which LLM produced the result. The model name comes from
the server-side LLM config (OPENAI_MODEL env var, default: llama3)
and is passed through the API response.

src/lib/llm.ts

@@ -21,6 +21,7 @@ export interface ConvertResult {
 	converted: string;
 	publicSystemPrompt: string;
 	publicUserMessage: string;
+	model: string;
 }
 
 const INPUT_TAG_START = '###### USER INPUT START ######';
@@ -102,6 +103,7 @@ export async function convertText(
 	return {
 		converted,
 		publicSystemPrompt: buildPublicSystemPrompt(styleModifier, intensityInstruction),
-		publicUserMessage: text
+		publicUserMessage: text,
+		model: merged.model
 	};
 }

src/lib/types.ts

@@ -24,6 +24,7 @@ export interface ConversionResponse {
 	intensity: number;
 	systemPrompt: string;
 	userMessage: string;
+	model: string;
 }
 
 export interface LLMConfig {