Allow deleting individual cache entries from the UI

[Rampim]

Summary

Currently the Cache tab only offers a Clear Cache button that wipes all entries at once. Users need the ability to delete individual cache entries — for example, to remove a stale or incorrect cached response without losing the entire cache.

Current Behavior

• The Cache tab shows a table of cached queries with ID, Query, SQL, Status, Uses, and Last Used
• The only delete option is Clear Cache, which removes all entries

Desired Behavior

• Add a delete action per row (e.g., a trash icon or delete button on each cache entry)
• Show a confirmation before deleting (similar to the existing Clear Cache confirmation modal)
• After deletion, refresh the cache table automatically

Implementation Notes

• Backend: Add a DELETE /api/gateways/{gateway_id}/cache/{cache_id} endpoint
• Frontend: Add a delete button/icon to each row in the cache table, with a confirmation step
• The delete should use the user's OAuth token (OBO) consistent with the auth model