feat(iot-hub): replace gateway download bar with inline markdown button

Instead of a fixed download bar above markdown, the creator writes
${gateway.downloadButton} anywhere in their markdown. It resolves to
an HTML button with data-action attribute. After markdown renders,
onMarkdownReady() attaches a click handler that calls the authenticated
DeviceService.downloadGatewayDockerComposeFile().

Usage in post-install.md:
  ${gateway.downloadButton}

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

@@ -76,18 +76,10 @@
               @switch (ws.type) {
 
                 @case ('instruction') {
-                  <div class="tb-device-install-instruction">
-                    @if (gatewayDockerComposeAvailable) {
-                      <div class="tb-gateway-download-bar">
-                        <span>{{ 'iot-hub.device-install-gateway-docker-compose' | translate }}</span>
-                        <button mat-stroked-button color="primary" (click)="downloadGatewayDockerCompose()">
-                          <mat-icon>download</mat-icon>
-                          {{ 'action.download' | translate }}
-                        </button>
-                      </div>
-                    }
+                  <div class="tb-device-install-instruction" #instructionContainer>
                     <tb-markdown [data]="ws.markdown"
-                                 [usePlainMarkdown]="true">
+                                 [usePlainMarkdown]="true"
+                                 (ready)="onMarkdownReady(instructionContainer)">
                     </tb-markdown>
                   </div>
                 }

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

@@ -123,22 +123,6 @@
   min-height: 120px;
 }
 
-// Gateway download bar
-.tb-gateway-download-bar {
-  display: flex;
-  align-items: center;
-  justify-content: space-between;
-  padding: 12px 16px;
-  margin-bottom: 16px;
-  background: #e3f2fd;
-  border-radius: 8px;
-
-  span {
-    font-size: 14px;
-    color: rgba(0, 0, 0, 0.87);
-  }
-}
-
 // Instruction view
 .tb-device-install-instruction {
   ::ng-deep tb-markdown {
@@ -151,6 +135,24 @@
         margin-top: 0;
       }
     }
+
+    .tb-download-btn {
+      display: inline-flex;
+      align-items: center;
+      gap: 4px;
+      padding: 6px 16px;
+      border: 1px solid #305680;
+      border-radius: 4px;
+      color: #305680;
+      font-size: 14px;
+      font-weight: 500;
+      text-decoration: none;
+      cursor: pointer;
+
+      &:hover {
+        background: rgba(48, 86, 128, 0.08);
+      }
+    }
   }
 }
 

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

@@ -240,16 +240,17 @@ export class TbDeviceInstallDialogComponent extends DialogComponent<TbDeviceInst
     }
   }
 
-  get gatewayDockerComposeAvailable(): boolean {
-    const gateway = this.entityOutputs.get('gateway');
-    return !!gateway?.dockerComposeUrl;
-  }
-
-  downloadGatewayDockerCompose(): void {
-    const gateway = this.entityOutputs.get('gateway');
-    if (gateway?.id) {
-      this.deviceService.downloadGatewayDockerComposeFile(gateway.id).subscribe();
-    }
+  onMarkdownReady(container: HTMLElement): void {
+    const buttons = container.querySelectorAll('[data-action="download-gateway-docker-compose"]');
+    buttons.forEach(btn => {
+      btn.addEventListener('click', (e) => {
+        e.preventDefault();
+        const gateway = this.entityOutputs.get('gateway');
+        if (gateway?.id) {
+          this.deviceService.downloadGatewayDockerComposeFile(gateway.id).subscribe();
+        }
+      });
+    });
   }
 
   getPatternErrorMessage(field: FormFieldDefinition): string {
@@ -266,6 +267,10 @@ export class TbDeviceInstallDialogComponent extends DialogComponent<TbDeviceInst
       if (key in this.transportVars) {
         return this.transportVars[key];
       }
+      // Special action placeholders
+      if (key === 'gateway.downloadButton') {
+        return '<a href="#" data-action="download-gateway-docker-compose" class="tb-download-btn">⬇ Download docker-compose.yml</a>';
+      }
       const dotIdx = key.indexOf('.');
       if (dotIdx > 0) {
         const alias = key.substring(0, dotIdx);