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-vue2/tailwind.config.js

@@ -0,0 +1,18 @@
+/** @type {import('tailwindcss').Config} */
+export default {
+  content: ['./src/**/*.{vue,js,ts,jsx,tsx}'],
+  important: '.markstream-vue2',
+  theme: {
+    extend: {
+      colors: {
+        'border': 'hsl(var(--border),214.3 21.44% 93.4%)',
+        'background': 'hsl(var(--background),0 0% 100%)',
+        'foreground': 'hsl(var(--foreground),217.2 22.08% 19.5%)',
+        'secondary': 'hsl(var(--secondary),214.3 21.44% 93.4%)',
+        'muted': 'hsl(var(--muted),210 28% 98.1%)',
+        'muted-foreground': 'hsl(var(--muted-foreground),215 12.16% 67.1%)',
+      },
+    },
+  },
+  plugins: [],
+}