Fechamento de Caixa - Tauri 2 initial commit

- Storage: SQLite local via rusqlite
- Supabase: REST API via reqwest
- Printer: USB ESC/POS for TM-T20
- Frontend: vanilla HTML (form-v9.3 ported)
- Build: GitHub Actions for Linux/Windows/macOS

src-tauri/build.rs

@@ -0,0 +1,3 @@
+fn main() {
+    tauri_build::build()
+}