Refactor application to MVC architecture with Flask blueprints

Major architectural refactoring to improve code organization, maintainability, and scalability:

- Implement MVC pattern with clear separation of concerns
- Organize code into blueprints for different functional areas (main, tenant, admin, api)
- Create models layer to encapsulate all database operations
- Create services layer for business logic (auth, product, barcode)
- Implement application factory pattern for better testability
- Add environment-based configuration management
- Remove old monolithic app.py and consolidate routes

New structure:
- app/models/ - Database operations (Tenant, Product, ARField, Settings)
- app/services/ - Business logic (Auth, Product, Barcode services)
- app/blueprints/ - Controllers organized by function
- app/config.py - Environment configurations
- run.py - Application entry point

All routes remain backward compatible. No changes to API or templates functionality.

src/app/models/ar_field.py

@@ -0,0 +1,84 @@
+from typing import Dict, List, Any
+from .base import get_db
+
+class ARFieldModel:
+    """Model for custom AR field operations"""
+
+    @staticmethod
+    def get_all(tenant_id: str) -> List[Dict[str, Any]]:
+        """Get all custom AR fields for a tenant"""
+        tenant_id = tenant_id.lower()
+
+        with get_db() as conn:
+            cursor = conn.cursor()
+            cursor.execute('''
+                SELECT id, field_name, label, field_type, editable, display_order
+                FROM custom_ar_fields
+                WHERE tenant_id = ?
+                ORDER BY display_order, id
+            ''', (tenant_id,))
+
+            fields = []
+            for row in cursor.fetchall():
+                fields.append({
+                    'id': row['id'],
+                    'fieldName': row['field_name'],
+                    'label': row['label'],
+                    'fieldType': row['field_type'],
+                    'editable': row['editable'],
+                    'displayOrder': row['display_order']
+                })
+
+            return fields
+
+    @staticmethod
+    def save(tenant_id: str, field_data: Dict[str, Any]):
+        """Save or update a custom AR field"""
+        tenant_id = tenant_id.lower()
+
+        with get_db() as conn:
+            cursor = conn.cursor()
+
+            if 'id' in field_data and field_data['id']:
+                # Update existing field
+                cursor.execute('''
+                    UPDATE custom_ar_fields
+                    SET field_name = ?, label = ?, field_type = ?, editable = ?,
+                        display_order = ?, updated_at = CURRENT_TIMESTAMP
+                    WHERE id = ? AND tenant_id = ?
+                ''', (
+                    field_data['fieldName'],
+                    field_data['label'],
+                    field_data['fieldType'],
+                    field_data['editable'],
+                    field_data['displayOrder'],
+                    field_data['id'],
+                    tenant_id
+                ))
+            else:
+                # Insert new field
+                cursor.execute('''
+                    INSERT INTO custom_ar_fields
+                    (tenant_id, field_name, label, field_type, editable, display_order)
+                    VALUES (?, ?, ?, ?, ?, ?)
+                ''', (
+                    tenant_id,
+                    field_data['fieldName'],
+                    field_data['label'],
+                    field_data['fieldType'],
+                    field_data['editable'],
+                    field_data['displayOrder']
+                ))
+
+            conn.commit()
+
+    @staticmethod
+    def delete(tenant_id: str, field_id: int):
+        """Delete a custom AR field"""
+        tenant_id = tenant_id.lower()
+
+        with get_db() as conn:
+            cursor = conn.cursor()
+            cursor.execute('DELETE FROM custom_ar_fields WHERE id = ? AND tenant_id = ?',
+                          (field_id, tenant_id))
+            conn.commit()