fix: stale chunk auto-reload + image paste upload UX

- Add lazyWithRetry wrapper for all lazy-loaded routes to auto-reload
  on stale chunk errors after deploys (prevents ErrorBoundary flash)
- Show toast notification when image paste/upload fails due to storage
  not configured (503), instead of silent tiny error thumbnails
- Remove failed uploads from thumbnail strip on 503 (was showing
  confusing retry icon)
- Pass completed upload IDs in navigation state from dashboard input
- Suppress Sentry dialog for chunk load errors (deploy artifacts)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/pages/AssistantChatPage.tsx

@@ -305,8 +305,13 @@ export default function AssistantChatPage() {
           setPendingUploads((prev) => prev.map((u) => u.id === upload.id ? { ...u, status: 'done' as const, result } : u))
         })
         .catch((err) => {
-          const errorMsg = err?.response?.status === 503 ? 'File uploads not available' : err?.message || 'Upload failed'
-          setPendingUploads((prev) => prev.map((u) => u.id === upload.id ? { ...u, status: 'error' as const, error: errorMsg } : u))
+          const is503 = err?.response?.status === 503
+          if (is503) {
+            toast.warning('Image attachments are not available yet — describe the issue in text instead')
+          } else {
+            toast.error(`Upload failed: ${err?.message || 'Unknown error'}`)
+          }
+          setPendingUploads((prev) => prev.filter((u) => u.id !== upload.id))
         })
     })
   }, [])