fix(linux): make the Confirm Before Deleting Rows switch take effect

[datlechin]

Why

Preferences showed a Confirm Before Deleting Rows switch that nothing read. Its description promised confirmations for dropping tables and discarding edits that never existed. Separately, a save landing after the user closed the Edit Connection dialog closed it again, and libadwaita logged a critical.

Change

• The switch now controls the one confirmation row deletes have: deleting 10 or more rows at once in a table tab. A delete only marks rows until Save, and Undo brings them back, so smaller deletes never ask, per the GNOME HIG. Drop Table always asks.
• The key is renamed confirm-bulk-delete, read at each delete, so a change reaches open tabs. The row's subtitle states the threshold.
• The connect dialog remembers it was closed, and a save that lands later leaves it alone. The connect dialog tests now present the dialog and make criticals fatal around the click.

Verified

The two browse tab tests and the late-save test fail before the fix and pass after. The full gtk suite and the storage tests pass, and fmt and both clippy runs are clean.