ui(table): DDL loading overlay must always pop

[ZhuchkaTriplesix]

Parent

Part of #445

Severity

High

Problem

Non-dismissible DDL spinner is shown via showAppDialog(barrierDismissible: false), then if (!mounted) return without Navigator.pop. Navigating away mid-fetch leaves a blocking overlay (and Escape cannot dismiss — see dialog Escape issue).

Evidence

• lib/features/extensions/extension_table_view.dart (~179–195)
• lib/features/sqlite/sqlite_table_view.dart (~194–207)
• Check postgres/mysql table DDL paths for the same pattern

Acceptance

• Loading route always popped in finally (or equivalent), even if widget unmounted
• Failed DDL fetch still clears spinner and surfaces error
• Widget/integration test or regression test for dispose-during-fetch

Suggested fix

Capture navigator before await; try/finally { if (navigator.canPop()) navigator.pop(); }.

[ZhuchkaTriplesix]

Shipped on dev via #459 (Closes did not auto-close because PRs targeted dev).