ui(dialog): Escape / barrierDismissible for showAppDialog

[ZhuchkaTriplesix]

Parent

Part of #445

Severity

High

Problem

showAppDialog always passes barrierDismissible: false to showGeneralDialog. Backdrop tap is handled manually via _BlurredDialogScaffold, but Escape never dismisses Preferences, About, connection forms, SQL history, etc.

Evidence

• lib/shared/widgets/app_dialog.dart (~18–20, scaffold)
• test/shared/app_dialog_test.dart — backdrop covered, Escape not covered

Acceptance

• When barrierDismissible: true (default), Escape closes the dialog
• When barrierDismissible: false, Escape does not close
• Widget test for Escape dismiss / non-dismiss

Suggested fix

Shortcuts / Actions / PopScope on the dialog scaffold; honor the public barrierDismissible flag for keyboard as well as backdrop.

[ZhuchkaTriplesix]

Shipped on dev via #458 (Closes did not auto-close because PRs targeted dev).