feat(devicemanager): add selector-based device APIs, selectFeature helper, convenience discovery methods, and ESCL scan completion fallback

ts/device/device.classes.device.ts

@@ -246,12 +246,35 @@ export class UniversalDevice extends plugins.events.EventEmitter {
   }
 
   /**
-   * Get a feature by type
+   * Get a feature by type (returns undefined if not available)
    */
   public getFeature<T extends Feature>(type: TFeatureType): T | undefined {
     return this._features.get(type) as T | undefined;
   }
 
+  /**
+   * Select a feature by type (throws if not available).
+   * Use this when you expect the device to have this feature and want fail-fast behavior.
+   *
+   * @param type The feature type to select
+   * @returns The feature instance
+   * @throws Error if the device does not have this feature
+   *
+   * @example
+   * ```typescript
+   * const scanFeature = device.selectFeature<ScanFeature>('scan');
+   * await scanFeature.connect();
+   * const result = await scanFeature.scan({ source: 'flatbed' });
+   * ```
+   */
+  public selectFeature<T extends Feature>(type: TFeatureType): T {
+    const feature = this._features.get(type) as T | undefined;
+    if (!feature) {
+      throw new Error(`Device '${this.name}' does not have feature '${type}'`);
+    }
+    return feature;
+  }
+
   /**
    * Get all features
    */