Add guidance message for non-customers before onboarding redirect

Non-customers attempting to use customer-only features (troubleshoot,
billing, asset) now see a friendly explanation before being handed off
to the onboarding agent.

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

src/routes/handlers/message-handler.ts

@@ -103,6 +103,10 @@ export async function handleMessage(
       const isCustomer = await checkIsCustomer(env.DB, telegramUserId);
       if (!isCustomer) {
         logger.info('비고객 → 온보딩 전환', { intent, telegramUserId });
+        await sendMessage(
+          env.BOT_TOKEN, chatId,
+          getMessage(lang, 'error_customer_only')
+        );
         const response = await onboardingAgent.processConsultation(env.DB, telegramUserId, text, env, meta);
         const { cleanText, sessionEnded } = cleanSessionMarkers(response);
         await storeConversation(env.DB, user.id, text, cleanText, requestId);