Enables balance payments via invoice

Adds functionality for users to pay their Castle balance by generating and paying a Lightning invoice.
This includes:
- Adding API endpoints for invoice generation and payment recording.
- Updating the frontend to allow users to initiate the invoice payment process.
- Passing the wallet's `inkey` to the frontend for payment status checks.

models.py

@@ -153,3 +153,15 @@ class CreateManualPaymentRequest(BaseModel):
 
     amount: int
     description: str
+
+
+class GeneratePaymentInvoice(BaseModel):
+    """Generate payment invoice request"""
+
+    amount: int
+
+
+class RecordPayment(BaseModel):
+    """Record a payment"""
+
+    payment_hash: str