Add sync backend infrastructure and improve grid snapping

- Add haexSyncBackends table with CRDT support for multi-backend sync
- Implement useSyncBackendsStore for managing sync server configurations
- Fix desktop icon grid snapping for all icon sizes (small to extra-large)
- Add Supabase client dependency for future sync implementation
- Generate database migration for sync_backends table

package.json

@@ -24,6 +24,7 @@
     "@nuxt/ui": "4.1.0",
     "@nuxtjs/i18n": "10.0.6",
     "@pinia/nuxt": "^0.11.2",
+    "@supabase/supabase-js": "^2.79.0",
     "@tailwindcss/vite": "^4.1.16",
     "@tauri-apps/api": "^2.9.0",
     "@tauri-apps/plugin-dialog": "^2.4.2",