Fix multi-plate thumbnail display in queue and add archive plate browsing

- Queue now shows correct plate thumbnail based on selected plate_id
  (previously always showed plate 1 regardless of selection)
- Archive cards now support plate browsing for multi-plate 3MF files:
  - Left/right arrows to cycle through plates on hover
  - Dot indicators at bottom show current plate (clickable)
  - Lazy-loads plate data only when user hovers
- Added getArchivePlateThumbnail and getLibraryFilePlateThumbnail API methods

Closes #166

frontend/src/api/client.ts

@@ -1984,6 +1984,8 @@ export const api = {
       method: 'POST',
     }),
   getArchiveThumbnail: (id: number) => `${API_BASE}/archives/${id}/thumbnail?v=${Date.now()}`,
+  getArchivePlateThumbnail: (id: number, plateIndex: number) =>
+    `${API_BASE}/archives/${id}/plate-thumbnail/${plateIndex}`,
   getArchiveDownload: (id: number) => `${API_BASE}/archives/${id}/download`,
   getArchiveGcode: (id: number) => `${API_BASE}/archives/${id}/gcode`,
   getArchivePlatePreview: (id: number) => `${API_BASE}/archives/${id}/plate-preview`,
@@ -3041,6 +3043,8 @@ export const api = {
     request<{ status: string; message: string }>(`/library/files/${id}`, { method: 'DELETE' }),
   getLibraryFileDownloadUrl: (id: number) => `${API_BASE}/library/files/${id}/download`,
   getLibraryFileThumbnailUrl: (id: number) => `${API_BASE}/library/files/${id}/thumbnail`,
+  getLibraryFilePlateThumbnail: (id: number, plateIndex: number) =>
+    `${API_BASE}/library/files/${id}/plate-thumbnail/${plateIndex}`,
   getLibraryFileGcodeUrl: (id: number) => `${API_BASE}/library/files/${id}/gcode`,
   moveLibraryFiles: (fileIds: number[], folderId: number | null) =>
     request<{ status: string; moved: number }>('/library/files/move', {