feat: make MH Paid column inline-editable

Add PATCH /api/payments/:id/mh-paid-amount for direct value updates.
Clicking the MH Paid cell opens an input; Enter/blur saves and refreshes,
Escape cancels. Dash placeholder is also clickable to enter a value.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/Backend/src/routes/payments.ts

@@ -427,6 +427,34 @@ router.patch(
   }
 );
 
+// PATCH /api/payments/:id/mh-paid-amount
+router.patch(
+  "/:id/mh-paid-amount",
+  async (req: Request, res: Response): Promise<any> => {
+    try {
+      const userId = req.user?.id;
+      if (!userId) return res.status(401).json({ message: "Unauthorized" });
+
+      const paymentId = parseIntOrError(req.params.id, "Payment ID");
+      const raw = req.body.mhPaidAmount;
+      const mhPaidAmount = parseFloat(raw);
+      if (isNaN(mhPaidAmount) || mhPaidAmount < 0) {
+        return res.status(400).json({ message: "Invalid mhPaidAmount value" });
+      }
+
+      const updated = await prisma.payment.update({
+        where: { id: paymentId },
+        data: { mhPaidAmount, updatedById: userId },
+      });
+
+      return res.json({ ...updated, mhPaidAmount: Number(updated.mhPaidAmount) });
+    } catch (err: unknown) {
+      const message = err instanceof Error ? err.message : "Failed to update MH paid amount";
+      return res.status(500).json({ message });
+    }
+  }
+);
+
 // PATCH /api/payments/:id/mh-payment-check
 router.patch(
   "/:id/mh-payment-check",