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/tauri.conf.json

@@ -0,0 +1,63 @@
+{
+  "$schema": "https://schema.tauri.app/config/2",
+  "productName": "BoosAPI Desktop",
+  "version": "0.0.93",
+  "identifier": "lat.boos.desktop",
+  "build": {
+    "beforeDevCommand": "pnpm dev",
+    "devUrl": "http://localhost:1420",
+    "beforeBuildCommand": "pnpm build",
+    "frontendDist": "../dist"
+  },
+  "app": {
+    "windows": [
+      {
+        "title": "BoosAPI Desktop",
+        "width": 1200,
+        "height": 800,
+        "minWidth": 800,
+        "minHeight": 600,
+        "titleBarStyle": "Overlay",
+        "hiddenTitle": true,
+        "visible": false
+      }
+    ],
+    "security": {
+      "csp": "default-src 'self'; script-src 'self' blob: 'wasm-unsafe-eval'; style-src 'self' 'unsafe-inline'; img-src 'self' data: blob: https:; connect-src 'self' https: http://localhost:* http://127.0.0.1:*; font-src 'self' data:; worker-src 'self' blob:"
+    }
+  },
+  "bundle": {
+    "active": true,
+    "targets": "all",
+    "createUpdaterArtifacts": true,
+    "resources": [],
+    "icon": [
+      "icons/32x32.png",
+      "icons/128x128.png",
+      "icons/128x128@2x.png",
+      "icons/icon.icns",
+      "icons/icon.ico"
+    ],
+    "windows": {
+      "webviewInstallMode": {
+        "type": "embedBootstrapper",
+        "silent": true
+      }
+    }
+  },
+  "plugins": {
+    "deep-link": {
+      "desktop": {
+        "schemes": [
+          "boosapi"
+        ]
+      }
+    },
+    "updater": {
+      "pubkey": "dW50cnVzdGVkIGNvbW1lbnQ6IG1pbmlzaWduIHB1YmxpYyBrZXk6IDU2QzNGRjRBQkQ4QzlENDQKUldSRW5ZeTlTdi9EVm1CRnUyNWF4d3oxeS9qWmlIQm12VmIvWmdDSEZiR21rMm9hNWRVU2VUTU4K",
+      "endpoints": [
+        "https://github.com/Boos4721/boos-chat/releases/latest/download/latest.json"
+      ]
+    }
+  }
+}