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/src/commands/settings.rs

@@ -5,7 +5,8 @@ use tauri::State;
 
 const SETTINGS_COLS: &str = "vendor_name, vendor_address, vendor_email, vendor_phone, vendor_pan,
     vendor_gstin, vendor_state_code, logo_path, signature_path, default_bank_id, default_tax_rate,
-    default_tax_type, payment_terms_days, currency, onboarded, theme";
+    default_tax_type, payment_terms_days, currency, onboarded, theme, gst_registration, default_hsn_sac, signatory_name,
+    signatory_designation";
 
 fn map_settings(row: &Row) -> rusqlite::Result<Settings> {
     Ok(Settings {
@@ -25,6 +26,10 @@ fn map_settings(row: &Row) -> rusqlite::Result<Settings> {
         currency: row.get(13)?,
         onboarded: row.get::<_, i64>(14)? != 0,
         theme: row.get(15)?,
+        gst_registration: row.get(16)?,
+        default_hsn_sac: row.get(17)?,
+        signatory_name: row.get(18)?,
+        signatory_designation: row.get(19)?,
     })
 }
 
@@ -48,7 +53,8 @@ pub fn save_settings(state: State<AppState>, settings: Settings) -> Result<Setti
              vendor_pan = ?5, vendor_gstin = ?6, vendor_state_code = ?7, logo_path = ?8,
              signature_path = ?9, default_bank_id = ?10, default_tax_rate = ?11,
              default_tax_type = ?12, payment_terms_days = ?13, currency = ?14,
-             onboarded = ?15, theme = ?16
+             onboarded = ?15, theme = ?16, gst_registration = ?17, default_hsn_sac = ?18,
+             signatory_name = ?19, signatory_designation = ?20
            WHERE id = 1"#,
         params![
             settings.vendor_name,
@@ -67,6 +73,10 @@ pub fn save_settings(state: State<AppState>, settings: Settings) -> Result<Setti
             settings.currency,
             if settings.onboarded { 1 } else { 0 },
             settings.theme,
+            settings.gst_registration,
+            settings.default_hsn_sac,
+            settings.signatory_name,
+            settings.signatory_designation,
         ],
     )
     .map_err(|e| e.to_string())?;