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/ImageNode/ImageNode.component.ts

@@ -0,0 +1,34 @@
+import type { AngularRenderableNode } from '../shared/node-helpers'
+import { ChangeDetectionStrategy, Component, Input } from '@angular/core'
+import { getString } from '../shared/node-helpers'
+
+@Component({
+  selector: 'markstream-angular-image-node',
+  standalone: true,
+  template: `
+    <img
+      class="image-node__img"
+      [attr.src]="src"
+      [attr.alt]="alt"
+      [attr.title]="title || null"
+      [attr.loading]="'lazy'"
+      decoding="async"
+    >
+  `,
+  changeDetection: ChangeDetectionStrategy.OnPush,
+})
+export class ImageNodeComponent {
+  @Input({ required: true }) node!: AngularRenderableNode
+
+  get src() {
+    return getString((this.node as any)?.src)
+  }
+
+  get alt() {
+    return getString((this.node as any)?.alt)
+  }
+
+  get title() {
+    return getString((this.node as any)?.title)
+  }
+}