feat(iot-hub): add image gallery placeholder for markdown instructions

Add ${images.gallery(path1,path2,path3)} template syntax that renders
multiple ZIP images as a side-by-side gallery in instruction steps.
Images are resolved from zipImages (base64 data URIs). Click to expand
individual images. Styled as a flex row with thumbnails.

ui-ngx/src/app/modules/home/components/iot-hub/device-install-dialog/device-install-dialog.component.scss

@@ -153,6 +153,31 @@
         background: rgba(48, 86, 128, 0.08);
       }
     }
+
+    .tb-gallery {
+      display: flex;
+      flex-wrap: wrap;
+      gap: 8px;
+      margin: 12px 0;
+    }
+
+    .tb-gallery-img {
+      max-height: 160px;
+      border-radius: 4px;
+      border: 1px solid rgba(0, 0, 0, 0.12);
+      cursor: pointer;
+      transition: max-height 0.2s ease;
+      object-fit: contain;
+
+      &:hover {
+        border-color: rgba(0, 0, 0, 0.24);
+      }
+
+      &.tb-gallery-img-expanded {
+        max-height: none;
+        max-width: 100%;
+      }
+    }
   }
 }
 

ui-ngx/src/app/modules/home/components/iot-hub/device-install-dialog/device-install-dialog.component.ts

@@ -251,12 +251,12 @@ export class TbDeviceInstallDialogComponent extends DialogComponent<TbDeviceInst
   }
 
   onMarkdownReady(container: HTMLElement): void {
+    // Download button handlers
     const buttons = container.querySelectorAll('[data-action="download-gateway-docker-compose"]');
     buttons.forEach(btn => {
       btn.addEventListener('click', (e) => {
         e.preventDefault();
         if (this.gatewayDockerComposeContent) {
-          // Custom template from ZIP — download as Blob
           const blob = new Blob([this.gatewayDockerComposeContent], { type: 'application/x-yaml' });
           const url = URL.createObjectURL(blob);
           const link = document.createElement('a');
@@ -265,7 +265,6 @@ export class TbDeviceInstallDialogComponent extends DialogComponent<TbDeviceInst
           link.click();
           URL.revokeObjectURL(url);
         } else {
-          // Standard template — authenticated API call
           const gateway = this.entityOutputs.get('gateway');
           if (gateway?.id) {
             this.deviceService.downloadGatewayDockerComposeFile(gateway.id).subscribe();
@@ -273,6 +272,13 @@ export class TbDeviceInstallDialogComponent extends DialogComponent<TbDeviceInst
         }
       });
     });
+    // Gallery image click-to-expand
+    const galleryImages = container.querySelectorAll('.tb-gallery-img');
+    galleryImages.forEach(img => {
+      img.addEventListener('click', () => {
+        img.classList.toggle('tb-gallery-img-expanded');
+      });
+    });
   }
 
   resolveImagePath(path: string): string {
@@ -300,6 +306,17 @@ export class TbDeviceInstallDialogComponent extends DialogComponent<TbDeviceInst
       if (key === 'gateway.downloadButton') {
         return '<a href="#" data-action="download-gateway-docker-compose" class="tb-download-btn">⬇ Download docker-compose.yml</a>';
       }
+      // Image gallery: ${images.gallery(path1,path2,path3)}
+      const galleryMatch = key.match(/^images\.gallery\((.+)\)$/);
+      if (galleryMatch) {
+        const paths = galleryMatch[1].split(',').map(p => p.trim());
+        const images = paths
+          .map(p => this.zipImages.get(p))
+          .filter(src => !!src)
+          .map(src => `<img src="${src}" class="tb-gallery-img" />`)
+          .join('');
+        return `<div class="tb-gallery">${images}</div>`;
+      }
       const dotIdx = key.indexOf('.');
       if (dotIdx > 0) {
         const alias = key.substring(0, dotIdx);