fix: resolve architecture validation violations

- Add invoice exceptions module with proper exception hierarchy
- Replace HTTPException with service-layer exceptions in invoice API
- Add InvoicePDFGeneratedResponse and InvoiceStatsResponse Pydantic models
- Replace db.commit() with db.flush() in services for proper transaction control
- Update invoice service to use exceptions from app/exceptions/invoice.py

All 14 errors and 14 warnings are now resolved. Validation passes with
only INFO-level findings.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/services/invoice_service.py

@@ -25,9 +25,17 @@ from sqlalchemy import and_, func
 from sqlalchemy.orm import Session
 
 from app.exceptions import (
-    OrderNotFoundException,
     ValidationException,
 )
+from app.exceptions.invoice import (
+    InvoiceNotFoundException,
+    InvoicePDFGenerationException,
+    InvoicePDFNotFoundException,
+    InvoiceSettingsAlreadyExistException,
+    InvoiceSettingsNotFoundException,
+    InvoiceValidationException,
+    OrderNotFoundException,
+)
 from models.database.invoice import (
     Invoice,
     InvoiceStatus,
@@ -89,18 +97,6 @@ LU_VAT_RATES = {
 }
 
 
-class InvoiceNotFoundException(Exception):
-    """Raised when invoice not found."""
-
-    pass
-
-
-class InvoiceSettingsNotFoundException(Exception):
-    """Raised when vendor invoice settings not found."""
-
-    pass
-
-
 class InvoiceService:
     """Service for invoice operations."""
 
@@ -205,9 +201,7 @@ class InvoiceService:
         """Get vendor invoice settings or raise exception."""
         settings = self.get_settings(db, vendor_id)
         if not settings:
-            raise InvoiceSettingsNotFoundException(
-                f"Invoice settings not configured for vendor {vendor_id}"
-            )
+            raise InvoiceSettingsNotFoundException(vendor_id)
         return settings
 
     def create_settings(
@@ -229,7 +223,7 @@ class InvoiceService:
             **data.model_dump(),
         )
         db.add(settings)
-        db.commit()
+        db.flush()
         db.refresh(settings)
 
         logger.info(f"Created invoice settings for vendor {vendor_id}")
@@ -249,7 +243,7 @@ class InvoiceService:
             setattr(settings, key, value)
 
         settings.updated_at = datetime.now(UTC)
-        db.commit()
+        db.flush()
         db.refresh(settings)
 
         logger.info(f"Updated invoice settings for vendor {vendor_id}")
@@ -278,7 +272,7 @@ class InvoiceService:
             is_vat_registered=bool(vendor.effective_tax_number),
         )
         db.add(settings)
-        db.commit()
+        db.flush()
         db.refresh(settings)
 
         logger.info(f"Created invoice settings from vendor data for vendor {vendor.id}")
@@ -435,7 +429,7 @@ class InvoiceService:
         )
 
         db.add(invoice)
-        db.commit()
+        db.flush()
         db.refresh(invoice)
 
         logger.info(
@@ -465,7 +459,7 @@ class InvoiceService:
         """Get invoice by ID or raise exception."""
         invoice = self.get_invoice(db, vendor_id, invoice_id)
         if not invoice:
-            raise InvoiceNotFoundException(f"Invoice {invoice_id} not found")
+            raise InvoiceNotFoundException(invoice_id)
         return invoice
 
     def get_invoice_by_number(
@@ -539,7 +533,7 @@ class InvoiceService:
 
         invoice.status = new_status
         invoice.updated_at = datetime.now(UTC)
-        db.commit()
+        db.flush()
         db.refresh(invoice)
 
         logger.info(f"Updated invoice {invoice.invoice_number} status to {new_status}")