fix(toolbar): omit inert when batch actions are not present

[metonym]

Fixes #2404

Fixes a regression caused by #2359 where ToolbarContent was incorrectly made inert when rows were selected in a DataTable, even when no ToolbarBatchActions component was present. This prevented users from interacting with toolbar controls, such as search inputs and buttons, when rows were selected.

Previously, ToolbarContent checked for selected row IDs from the DataTable context to determine if it should be inert. However, this caused issues when a DataTable had row selection enabled but no batch actions component. The fix tracks the actual visibility state of batch actions through a new batchActionsActive store in the Toolbar context, ensuring toolbar content is only inert when batch actions are actually visible.

Example of affected usage:

<DataTable {headers} {rows} bind:selectedRowIds>
  <Toolbar>
    <ToolbarContent>
      <ToolbarSearch persistent />
      <Button>Action</Button>
    </ToolbarContent>
  </Toolbar>
</DataTable>

Changes

• Add batchActionsActive writable store to Toolbar context to track batch actions visibility state
• Update ToolbarBatchActions to set batchActionsActive based on whether batch actions are shown
• Update ToolbarContent to subscribe to batchActionsActive instead of checking batchSelectedIds from DataTable context