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/src-tauri/capabilities/default.json

@@ -0,0 +1,32 @@
+{
+  "$schema": "../gen/schemas/desktop-schema.json",
+  "identifier": "default",
+  "description": "Capability for the main window",
+  "windows": ["main"],
+  "permissions": [
+    "core:default",
+    "core:window:allow-start-dragging",
+    "core:window:allow-show",
+    "core:window:allow-hide",
+    "core:window:allow-close",
+    "core:window:allow-set-focus",
+    "deep-link:default",
+    "opener:default",
+    "dialog:default",
+    "fs:default",
+    "process:default",
+    "global-shortcut:allow-register",
+    "global-shortcut:allow-unregister",
+    "global-shortcut:allow-unregister-all",
+    "global-shortcut:allow-is-registered",
+    "autostart:default",
+    "fs:allow-write-text-file",
+    "fs:allow-write-file",
+    "fs:allow-read-file",
+    "mcp-bridge:default",
+    "updater:default",
+    "clipboard-manager:allow-write-text",
+    "clipboard-manager:allow-read-text",
+    "clipboard-manager:allow-write-image"
+  ]
+}