fix: accumulate streaming AI text parts instead of replacing

vite.config.ts

@@ -123,7 +123,7 @@ function apiSavePlugin() {
                   const event = JSON.parse(line)
                   if (!resolvedSessionId && event.sessionID) resolvedSessionId = event.sessionID
                   if (event.type === 'text' && event.part?.text) {
-                    aiText = event.part.text
+                    aiText += event.part.text
                   }
                 } catch { continue }
               }