Add user onboarding, keyboard overlay, and DB support

Introduce first-time user onboarding and a navigable on-screen keyboard, plus persistent user storage via a bundled rusqlite database and Tauri API. Backend: add rusqlite dependency, DB initialization in tauri setup, schema migration/backfill for users, and two Tauri commands (get_first_user, create_user) with input sanitization and structured UserRecord. Frontend: add core/users.js (invoke + localStorage fallback), integrate user state initialization, add user setup view/styles and keyboard overlay (JS/CSS), wire views and navigation to show onboarding when needed, and update lock view behavior to coordinate onboarding and passkey flow. Also add @tauri-apps/api dependency and update package/Cargo lock files accordingly.

package.json

@@ -12,6 +12,7 @@
     "@tauri-apps/cli": "^2"
   },
   "dependencies": {
-    "@nebulaproject/core": "^0.1.3"
+    "@nebulaproject/core": "^0.1.3",
+    "@tauri-apps/api": "^2.10.1"
   }
 }