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/tailwind.preset.js

@@ -0,0 +1,46 @@
+/**
+ * Shared Tailwind preset for markstream-vue.
+ *
+ * Maps Tailwind utilities to --ms-* design tokens so that rounded-*,
+ * font-*, and color utilities respond to theme switching.
+ *
+ * Usage (consumer):
+ *   import markstreamPreset from 'markstream-vue/tailwind.preset'
+ *   export default { presets: [markstreamPreset], ... }
+ */
+
+/** @type {import('tailwindcss').Config} */
+export default {
+  theme: {
+    extend: {
+      colors: {
+        'background': 'hsl(var(--ms-background))',
+        'foreground': 'hsl(var(--ms-foreground))',
+        'muted': 'hsl(var(--ms-muted))',
+        'muted-foreground': 'hsl(var(--ms-muted-foreground))',
+        'secondary': 'hsl(var(--ms-secondary))',
+        'secondary-foreground': 'hsl(var(--ms-secondary-foreground))',
+        'accent': 'hsl(var(--ms-accent))',
+        'accent-foreground': 'hsl(var(--ms-accent-foreground))',
+        'primary': 'hsl(var(--ms-primary))',
+        'primary-foreground': 'hsl(var(--ms-primary-foreground))',
+        'destructive': 'hsl(var(--ms-destructive))',
+        'destructive-foreground': 'hsl(var(--ms-destructive-foreground))',
+        'border': 'hsl(var(--ms-border))',
+        'ring': 'hsl(var(--ms-ring))',
+        'popover': 'hsl(var(--ms-popover))',
+        'popover-foreground': 'hsl(var(--ms-popover-foreground))',
+      },
+      borderRadius: {
+        lg: 'var(--ms-radius)',
+        md: 'calc(var(--ms-radius) * 0.75)',
+        DEFAULT: 'calc(var(--ms-radius) * 0.5)',
+        sm: 'calc(var(--ms-radius) * 0.33)',
+      },
+      fontFamily: {
+        sans: ['var(--ms-font-sans)'],
+        mono: ['var(--ms-font-mono)'],
+      },
+    },
+  },
+}