fix: remove redundant async dispatch, guard switchDatabase result

[datlechin]

Summary

• RightPanelState.isPresented didSet — removed redundant DispatchQueue.main.async { [self] in ... }. The didSet already runs on @MainActor, so the async dispatch was unnecessary and created a brief strong self-capture.
• DatabaseManager.switchDatabase — replaced try? with do/catch. Previously, if restoring the saved database failed, currentDatabase was set to the saved value anyway, making the UI show a database the connection wasn't actually on. Now only updates currentDatabase on success and logs the failure.

Test plan

• Toggle right panel open/close — verify state persists across app launches
• Connect to MSSQL with a saved last-database — verify database restores correctly
• Connect to MSSQL with a deleted/renamed saved database — verify graceful fallback (default database shown, warning logged)