Add versioned DB migrations, startup error dialog and native basics

rusqlite_migration with a VACUUM INTO backup before upgrading; M2 adds GST
registration, snapshot, cancellation and draft columns and backfills
snapshots for existing invoices. Startup failures now show a native dialog
instead of exiting silently. Adds single-instance and window-state plugins,
minimum window 960x600, embedBootstrapper, DMABUF workaround on Linux and
xbps dependency updates.

src-tauri/Cargo.toml

@@ -4,7 +4,7 @@ version = "0.1.0"
 description = "Voiced — offline invoicing desktop app by Bongbetic"
 authors = ["Bongbetic"]
 edition = "2021"
-rust-version = "1.77"
+rust-version = "1.95"
 
 # The `_lib` suffix keeps the library name distinct from the binary name on Windows.
 [lib]
@@ -21,11 +21,20 @@ tauri-plugin-opener = "2"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 rusqlite = { version = "0.40", features = ["bundled"] }
+rusqlite_migration = "2.6"
 chrono = { version = "0.4", features = ["serde"] }
 uuid = { version = "1", features = ["v4"] }
 thiserror = "2"
 base64 = "0.22"
 
+# Desktop-only plugins (not available on mobile targets).
+[target.'cfg(not(any(target_os = "android", target_os = "ios")))'.dependencies]
+tauri-plugin-single-instance = "2"
+tauri-plugin-window-state = "2"
+
+[dev-dependencies]
+tempfile = "3"
+
 [features]
 # Production builds embed the frontend and serve it over the custom asset
 # protocol. Without this, the app expects a dev server on localhost:1420.