Adds balance payment feature

Implements a feature that allows users to pay their outstanding balance via Lightning.

The changes include:
- Adds the UI elements for invoice generation and display, including QR code.
- Integrates backend endpoints to generate and record payments.
- Adds polling mechanism to track payments and update balance.
- Creates new database models to support manual payment requests.

models.py

@@ -132,3 +132,24 @@ class StoredUserWalletSettings(UserWalletSettings):
     """Stored user wallet settings with user ID"""
 
     id: str  # user_id
+
+
+class ManualPaymentRequest(BaseModel):
+    """Manual payment request from user to castle"""
+
+    id: str
+    user_id: str
+    amount: int  # in satoshis
+    description: str
+    status: str = "pending"  # pending, approved, rejected
+    created_at: datetime
+    reviewed_at: Optional[datetime] = None
+    reviewed_by: Optional[str] = None  # user_id of castle admin who reviewed
+    journal_entry_id: Optional[str] = None  # set when approved
+
+
+class CreateManualPaymentRequest(BaseModel):
+    """Create a manual payment request"""
+
+    amount: int
+    description: str