fix: show actual error details in chat error messages

- Extract error from err.response.data.error (axios error response)
- Log full error to console for debugging
- Show actual backend error message instead of generic 'Error'

frontend/src/components/Step5Interaction.vue

@@ -669,10 +669,12 @@ const sendMessage = async () => {
       await sendToAgent(message)
     }
   } catch (err) {
-    addLog(t('log.sendFailed', { error: err.message }))
+    const errDetail = err.response?.data?.error || err.message || 'Unknown error'
+    console.error('Chat error:', err)
+    addLog(`❌ ${t('log.sendFailed', { error: errDetail })}`)
     chatHistory.value.push({
       role: 'assistant',
-      content: t('step5.errorOccurred', { error: err.message }),
+      content: `❌ ${t('step5.errorOccurred', { error: errDetail })}`,
       timestamp: new Date().toISOString()
     })
   } finally {