Remove Gesamt-Provision card from the Provisionen view

User doesn't need the third KPI tile. Drop it from the markup, drop
the matching #totalGesamtProvision write in updateProvisionenTable
and let the grid breathe with two columns instead of three. Revert
the backend total_gesamt_provision field to its original meaning
(shop + employee) since no consumer in the UI depends on it now.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

routes/provisionen.js

@@ -138,7 +138,7 @@ router.get('/provisionen', asyncHandler(async (req, res) => {
         total_provision: totalShop.toFixed(2),
         total_shop_provision: totalShop.toFixed(2),
         total_mitarbeiter_provision: totalMitarbeiter.toFixed(2),
-        total_gesamt_provision: (totalShop - totalMitarbeiter).toFixed(2),
+        total_gesamt_provision: (totalShop + totalMitarbeiter).toFixed(2),
     });
 }));