feat(mentor-workspace): inline document preview matching applicant docs pattern

- Eye toggle expands the row below to embed FilePreview from
  @/components/shared/file-viewer (PDF iframe, image, video, Office docs)
- Download button uses explicit Content-Disposition: attachment via a
  new `disposition` input on workspaceGetFileDownloadUrl
- getPresignedUrl learns `inline: true` and optional `response-content-type`
  override so PDFs/images don't get force-downloaded by MinIO's default
- Eye button only renders for previewable mime types

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/mentor/workspace-files-panel.tsx

@@ -12,8 +12,9 @@ import {
   AlertDialogDescription, AlertDialogFooter, AlertDialogHeader, AlertDialogTitle,
   AlertDialogTrigger,
 } from '@/components/ui/alert-dialog'
-import { FileText, Upload, Download, Trash2, MessageSquare } from 'lucide-react'
+import { Eye, FileText, Upload, Download, Trash2, MessageSquare, X, Loader2 } from 'lucide-react'
 import { formatDistanceToNow } from 'date-fns'
+import { FilePreview, isOfficeFile } from '@/components/shared/file-viewer'
 
 interface Props {
   /** Project the workspace belongs to — drives file list (project-scoped). */
@@ -90,10 +91,43 @@ export function WorkspaceFilesPanel({ projectId, mentorAssignmentId, asApplicant
     }
   }
 
+  const [previewFileId, setPreviewFileId] = useState<string | null>(null)
+  const [previewUrl, setPreviewUrl] = useState<string | null>(null)
+  const [previewLoading, setPreviewLoading] = useState(false)
+
+  const canPreviewMime = (m: string, name: string) =>
+    m.startsWith('video/') || m === 'application/pdf' || m.startsWith('image/') || isOfficeFile(m, name)
+
+  const togglePreview = async (file: { id: string; mimeType: string; fileName: string }) => {
+    if (previewFileId === file.id) {
+      setPreviewFileId(null)
+      setPreviewUrl(null)
+      return
+    }
+    setPreviewFileId(file.id)
+    setPreviewUrl(null)
+    setPreviewLoading(true)
+    try {
+      const { url } = await downloadMutation.mutateAsync({ mentorFileId: file.id, disposition: 'inline' })
+      setPreviewUrl(url)
+    } catch (err) {
+      toast.error(err instanceof Error ? err.message : 'Preview failed')
+      setPreviewFileId(null)
+    } finally {
+      setPreviewLoading(false)
+    }
+  }
+
   const handleDownload = async (mentorFileId: string) => {
     try {
-      const { url } = await downloadMutation.mutateAsync({ mentorFileId })
-      window.open(url, '_blank')
+      const { url } = await downloadMutation.mutateAsync({ mentorFileId, disposition: 'attachment' })
+      const a = document.createElement('a')
+      a.href = url
+      a.download = ''
+      a.rel = 'noopener'
+      document.body.appendChild(a)
+      a.click()
+      a.remove()
     } catch (err) {
       toast.error(err instanceof Error ? err.message : 'Download failed')
     }
@@ -148,8 +182,12 @@ export function WorkspaceFilesPanel({ projectId, mentorAssignmentId, asApplicant
         )}
 
         <ul className="divide-y">
-          {(files ?? []).map((f) => (
-            <li key={f.id} className="flex items-center gap-3 py-3">
+          {(files ?? []).map((f) => {
+            const isOpen = previewFileId === f.id
+            const previewable = canPreviewMime(f.mimeType, f.fileName)
+            return (
+            <li key={f.id} className="py-3 space-y-2">
+              <div className="flex items-center gap-3">
               <FileText className="h-5 w-5 text-muted-foreground shrink-0" />
               <div className="flex-1 min-w-0">
                 <div className="font-medium truncate">{f.fileName}</div>
@@ -167,7 +205,24 @@ export function WorkspaceFilesPanel({ projectId, mentorAssignmentId, asApplicant
                   <div className="text-xs text-muted-foreground mt-1">{f.description}</div>
                 )}
               </div>
-              <Button variant="ghost" size="icon" onClick={() => handleDownload(f.id)}>
+              {previewable && (
+                <Button
+                  variant="ghost"
+                  size="icon"
+                  onClick={() => togglePreview(f)}
+                  title={isOpen ? 'Close preview' : 'Preview'}
+                  aria-label={isOpen ? 'Close preview' : 'Preview file'}
+                >
+                  {isOpen ? <X className="h-4 w-4" /> : <Eye className="h-4 w-4" />}
+                </Button>
+              )}
+              <Button
+                variant="ghost"
+                size="icon"
+                onClick={() => handleDownload(f.id)}
+                title="Download"
+                aria-label="Download file"
+              >
                 <Download className="h-4 w-4" />
               </Button>
               <AlertDialog>
@@ -191,8 +246,22 @@ export function WorkspaceFilesPanel({ projectId, mentorAssignmentId, asApplicant
                   </AlertDialogFooter>
                 </AlertDialogContent>
               </AlertDialog>
+              </div>
+              {isOpen && (
+                <div className="rounded-md border bg-muted/30 overflow-hidden">
+                  {previewLoading || !previewUrl ? (
+                    <div className="flex items-center justify-center py-12 text-sm text-muted-foreground">
+                      <Loader2 className="h-4 w-4 mr-2 animate-spin" />
+                      Loading preview…
+                    </div>
+                  ) : (
+                    <FilePreview file={{ mimeType: f.mimeType, fileName: f.fileName }} url={previewUrl} />
+                  )}
+                </div>
+              )}
             </li>
-          ))}
+            )
+          })}
         </ul>
       </CardContent>
     </Card>