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/stream-monaco/examples/shiki-sync/src/App.vue

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+<script setup lang="ts">
+import type { ShikiHighlighter } from '../../../src'
+import { onMounted, ref } from 'vue'
+import { registerMonacoThemes, useMonaco } from '../../../src'
+
+const container = ref<HTMLElement | null>(null)
+const preview = ref<HTMLDivElement | null>(null)
+
+const allThemes = [
+  'andromeeda',
+  'aurora-x',
+  'ayu-dark',
+  'catppuccin-frappe',
+  'catppuccin-latte',
+  'catppuccin-macchiato',
+  'catppuccin-mocha',
+  'dark-plus',
+  'dracula',
+  'dracula-soft',
+  'everforest-dark',
+  'everforest-light',
+  'github-dark',
+  'github-dark-default',
+  'github-dark-dimmed',
+  'github-dark-high-contrast',
+  'github-light',
+  'github-light-default',
+  'github-light-high-contrast',
+  'gruvbox-dark-hard',
+  'gruvbox-dark-medium',
+  'gruvbox-dark-soft',
+  'gruvbox-light-hard',
+  'gruvbox-light-medium',
+  'gruvbox-light-soft',
+  'houston',
+  'kanagawa-dragon',
+  'kanagawa-lotus',
+  'kanagawa-wave',
+  'laserwave',
+  'light-plus',
+  'material-theme',
+  'material-theme-darker',
+  'material-theme-lighter',
+  'material-theme-ocean',
+  'material-theme-palenight',
+  'min-dark',
+  'min-light',
+  'monokai',
+  'night-owl',
+  'nord',
+  'one-dark-pro',
+  'one-light',
+  'plastic',
+  'poimandres',
+  'red',
+  'rose-pine',
+  'rose-pine-dawn',
+  'rose-pine-moon',
+  'slack-dark',
+  'slack-ochin',
+  'snazzy-light',
+  'solarized-dark',
+  'solarized-light',
+  'synthwave-84',
+  'tokyo-night',
+  'vesper',
+  'vitesse-black',
+  'vitesse-dark',
+  'vitesse-light',
+]
+const allLanguages = ['javascript']
+
+let shikiHighlighter: ShikiHighlighter | null = null
+const loading = ref(false)
+const error = ref<string | null>(null)
+const selectedTheme = ref<string>(allThemes[0])
+
+onMounted(async () => {
+  loading.value = true
+  error.value = null
+  try {
+    shikiHighlighter = await registerMonacoThemes(allThemes, allLanguages)
+  }
+  catch (e: any) {
+    error.value = e?.message || String(e)
+  }
+  finally {
+    loading.value = false
+  }
+})
+
+async function retryLoad() {
+  loading.value = true
+  error.value = null
+  try {
+    shikiHighlighter = await registerMonacoThemes(allThemes, allLanguages)
+  }
+  catch (e: any) {
+    error.value = e?.message || String(e)
+  }
+  finally {
+    loading.value = false
+  }
+}
+
+const { createEditor, setTheme } = useMonaco({
+  themes: allThemes,
+  languages: allLanguages,
+  theme: selectedTheme.value,
+})
+
+onMounted(async () => {
+  if (container.value) {
+    await createEditor(container.value, 'console.log("hello world")', 'javascript')
+    // apply initial theme to preview once editor created
+    applyShikiRender(selectedTheme.value)
+  }
+})
+
+function applyShikiRender(themeName: string) {
+  if (!shikiHighlighter || !preview.value)
+    return
+
+  try {
+    const html = shikiHighlighter.codeToHtml('console.log("hello world")', { lang: 'javascript', theme: themeName })
+    preview.value.innerHTML = html
+  }
+  catch {
+    try {
+      shikiHighlighter.setTheme(themeName)
+    }
+    catch { }
+  }
+}
+
+function onThemeChange(theme: string) {
+  selectedTheme.value = theme
+  setTheme(theme)
+  applyShikiRender(theme)
+}
+
+function onThemeSelectChange(e: Event) {
+  const el = e.target as HTMLSelectElement | null
+  if (!el)
+    return
+  onThemeChange(el.value)
+}
+</script>
+
+<template>
+  <div style="padding:16px">
+    <div class="controls">
+      <label for="theme-select">Theme:</label>
+      <select id="theme-select" v-model="selectedTheme" :disabled="loading || !!error" @change="onThemeSelectChange">
+        <option v-for="t in allThemes" :key="t" :value="t">
+          {{ t }}
+        </option>
+      </select>
+      <span v-if="loading" style="margin-left:8px">Loading themes...</span>
+      <span v-if="error" style="margin-left:8px;color:crimson">Error: {{ error }}</span>
+      <button v-if="error" style="margin-left:8px" @click="retryLoad">
+        Retry
+      </button>
+    </div>
+
+    <div ref="container" style="height:300px;border:1px solid #ddd;margin-top:12px" />
+
+    <h3>Shiki preview</h3>
+    <div ref="preview" />
+  </div>
+</template>
+
+<style scoped>
+.controls { display:flex; gap:8px }
+</style>

desktop/libs/stream-monaco/examples/shiki-sync/src/main.ts

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+import { createApp } from 'vue'
+import App from './App.vue'
+import 'monaco-editor/min/vs/editor/editor.main.css'
+
+createApp(App).mount('#app')