Phase 0: Update credit costs and CreditService, add credit checks to AI Engine

- Updated CREDIT_COSTS to match Phase 0 spec (flat structure)
- Added get_credit_cost() method to CreditService
- Updated check_credits() to accept operation_type and amount
- Added deduct_credits_for_operation() convenience method
- Updated AI Engine to check credits BEFORE AI call
- Updated AI Engine to deduct credits AFTER successful execution
- Added helper methods for operation type mapping and amount calculation

backend/igny8_core/modules/billing/constants.py

@@ -1,22 +1,21 @@
 """
 Credit Cost Constants
+Phase 0: Credit-only system costs per operation
 """
 CREDIT_COSTS = {
-    'clustering': {
-        'base': 1,  # 1 credit per 30 keywords
-        'per_keyword': 1 / 30,
-    },
-    'ideas': {
-        'base': 1,  # 1 credit per idea
-    },
-    'content': {
-        'base': 3,  # 3 credits per full blog post
-    },
-    'images': {
-        'base': 1,  # 1 credit per image
-    },
-    'reparse': {
-        'base': 1,  # 1 credit per reparse
-    },
+    'clustering': 10,                    # Per clustering request
+    'idea_generation': 15,               # Per cluster → ideas request
+    'content_generation': 1,             # Per 100 words
+    'image_prompt_extraction': 2,        # Per content piece
+    'image_generation': 5,               # Per image
+    'linking': 8,                        # Per content piece (NEW)
+    'optimization': 1,                   # Per 200 words (NEW)
+    'site_structure_generation': 50,     # Per site blueprint (NEW)
+    'site_page_generation': 20,          # Per page (NEW)
+    # Legacy operation types (for backward compatibility)
+    'ideas': 15,                         # Alias for idea_generation
+    'content': 3,                        # Legacy: 3 credits per content piece
+    'images': 5,                          # Alias for image_generation
+    'reparse': 1,                        # Per reparse
 }