refactor(ui): tables, extensions and settings sections on QueryaButton - #1423

Part of #1337 / #1331 (closes neither). Continues #1420, #1421, #1422.

What

Shadcn button calls become QueryaButton in 14 files:

• Table toolbars: PostgreSQL, MySQL, SQLite and the generic table view, the staging toolbar and table_view_staging.
• The cell popover inspector of the grid.
• Extensions: table toolbar, table view, extension card and the driver recovery banner.
• The workspace empty hero and the preference sections (appearance, about, extensions).

Toolbars and panels are md; dense rows (ButtonSize.small, ButtonDensity.compact) are sm.

Beyond the mechanical replacement

• Loading: Save / Save Changes (staging toolbar), Save to DB (inspector) and Restart Driver (two places) use the button's loading instead of a spinner leading plus label switch.
• Icon-only: the compact Revert All is a QueryaButton.icon with a tooltip.
• Preference sections: OutlineButton(child: Row(Icon, SizedBox, Text)) becomes a labelled secondary button with an icon (10 buttons); the codemod learned this shape in this pass.

Tests

sql_workspace_readonly_save_test found Save Changes as PrimaryButton and read its onPressed; it now looks for QueryaButton (same onPressed, same enabled / disabled expectations).

Still shadcn

QueryaActionButton / QueryaActionMenu and the toolbars built on them (Execute (F5) finders in generic_sql_workspace_shortcuts_test, sql_workspace_execute_dirty_guard_test, extension_sql_workspace_test) are next: they need the action button itself swapped.

Not run locally; CI is the check.