refactor: Fix AI billing system - revert to commit #10 + fixes

- Reverted to commit #10 (98e68f6) for stable AI function base
- Fixed database migrations: removed 0018-0019 that broke schema
- Fixed CreditCostConfig schema: restored credits_cost, unit fields
- Fixed historical table schema for django-simple-history
- Added debug system (staged for future use)

Changes:
- CreditCostConfig: Updated OPERATION_TYPE_CHOICES (10 ops, no duplicates)
- CreditUsageLog: Updated choices with legacy aliases marked
- Migration 0018_update_operation_choices: Applied successfully
- All AI operations working (clustering, ideas, content, optimization, etc.)

Test Results:
✓ CreditCostConfig save/load working
✓ Credit check passing for all operations
✓ AICore initialization successful
✓ AIEngine operation mapping functional
✓ Admin panel accessible without 500 errors

Future: AI-MODEL-COST-REFACTOR-PLAN.md created for token-based system

backend/igny8_core/business/billing/models.py

@@ -75,10 +75,16 @@ class CreditUsageLog(AccountBaseModel):
         ('idea_generation', 'Content Ideas Generation'),
         ('content_generation', 'Content Generation'),
         ('image_generation', 'Image Generation'),
+        ('image_prompt_extraction', 'Image Prompt Extraction'),
+        ('linking', 'Internal Linking'),
+        ('optimization', 'Content Optimization'),
         ('reparse', 'Content Reparse'),
-        ('ideas', 'Content Ideas Generation'),  # Legacy
-        ('content', 'Content Generation'),  # Legacy
-        ('images', 'Image Generation'),  # Legacy
+        ('site_structure_generation', 'Site Structure Generation'),
+        ('site_page_generation', 'Site Page Generation'),
+        # Legacy aliases for backward compatibility (don't show in new dropdowns)
+        ('ideas', 'Content Ideas Generation (Legacy)'),
+        ('content', 'Content Generation (Legacy)'),
+        ('images', 'Image Generation (Legacy)'),
     ]
     
     operation_type = models.CharField(max_length=50, choices=OPERATION_TYPE_CHOICES, db_index=True)
@@ -112,11 +118,26 @@ class CreditCostConfig(models.Model):
     Configurable credit costs per AI function
     Admin-editable alternative to hardcoded constants
     """
+    
+    # Active operation types (excludes legacy aliases)
+    OPERATION_TYPE_CHOICES = [
+        ('clustering', 'Keyword Clustering'),
+        ('idea_generation', 'Content Ideas Generation'),
+        ('content_generation', 'Content Generation'),
+        ('image_generation', 'Image Generation'),
+        ('image_prompt_extraction', 'Image Prompt Extraction'),
+        ('linking', 'Internal Linking'),
+        ('optimization', 'Content Optimization'),
+        ('reparse', 'Content Reparse'),
+        ('site_structure_generation', 'Site Structure Generation'),
+        ('site_page_generation', 'Site Page Generation'),
+    ]
+    
     # Operation identification
     operation_type = models.CharField(
         max_length=50,
         unique=True,
-        choices=CreditUsageLog.OPERATION_TYPE_CHOICES,
+        choices=OPERATION_TYPE_CHOICES,
         help_text="AI operation type"
     )