feat(desktop): embed BoosAPI Desktop client as a subproject

Vendor the rebranded BoosAPI Desktop client (Tauri + Vue) into metapi as
a monorepo subdirectory under desktop/. Source only — node_modules,
dist, Cargo target and the upstream .git history are excluded.

desktop/ keeps its own independent Cargo workspace (desktop/src-tauri
with crates/*); it is not part of the backend boosapi crate, so a
`cargo check` at the metapi root still compiles only the backend. Build
the desktop app from desktop/src-tauri per desktop/README.md.

Note: app icons are still placeholder assets pending the final BoosAPI
logo. The updater signing keys live outside the repo and are not
included.

desktop/libs/markstream-vue/packages/markstream-angular/src/components/HighlightNode/HighlightNode.component.ts

@@ -0,0 +1,34 @@
+import type { AngularRenderableNode, AngularRenderContext } from '../shared/node-helpers'
+import { CommonModule } from '@angular/common'
+import { ChangeDetectionStrategy, Component, forwardRef, Input } from '@angular/core'
+import { NestedRendererComponent } from '../NestedRenderer/NestedRenderer.component'
+import { getNodeList } from '../shared/node-helpers'
+
+@Component({
+  selector: 'markstream-angular-highlight-node',
+  standalone: true,
+  imports: [CommonModule, forwardRef(() => NestedRendererComponent)],
+  template: `
+    <mark>
+      <markstream-angular-nested-renderer
+        [nodes]="children"
+        [context]="context"
+        [indexPrefix]="nestedPrefix"
+      />
+    </mark>
+  `,
+  changeDetection: ChangeDetectionStrategy.OnPush,
+})
+export class HighlightNodeComponent {
+  @Input({ required: true }) node!: AngularRenderableNode
+  @Input() context?: AngularRenderContext
+  @Input() indexKey?: string
+
+  get children() {
+    return getNodeList((this.node as any)?.children)
+  }
+
+  get nestedPrefix() {
+    return `${this.indexKey || 'highlight'}-highlight`
+  }
+}