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/components/dashboard/StartSessionInput.tsx

@@ -3,6 +3,7 @@ import { useNavigate } from 'react-router-dom'
 import { Send, Paperclip, Terminal, Loader2, X, RotateCcw, ImagePlus } from 'lucide-react'
 import { cn } from '@/lib/utils'
 import { uploadsApi } from '@/api/uploads'
+import { toast } from '@/lib/toast'
 import type { PendingUpload } from '@/types/upload'
 
 const SUGGESTIONS = [
@@ -44,6 +45,12 @@ export function StartSessionInput() {
     if (logContent.trim()) {
       state.logs = logContent.trim()
     }
+    const completedUploadIds = pendingUploads
+      .filter((u) => u.status === 'done' && u.result?.id)
+      .map((u) => u.result!.id)
+    if (completedUploadIds.length > 0) {
+      state.uploadIds = completedUploadIds
+    }
     navigate('/assistant', { state })
   }
 
@@ -81,12 +88,16 @@ export function StartSessionInput() {
           )
         })
         .catch((err) => {
-          const errorMsg = err?.response?.status === 503
+          const is503 = err?.response?.status === 503
+          const errorMsg = is503
             ? '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)
-          )
+          if (is503) {
+            toast.warning('Image attachments are not available yet — describe the issue in text instead')
+          } else {
+            toast.error(`Upload failed: ${errorMsg}`)
+          }
+          setPendingUploads((prev) => prev.filter((u) => u.id !== upload.id))
         })
     })
   }, [])