Fix image generation model and purge logic

- Change NanoBanana Pro model from gemini-3-pro-image-preview to gemini-2.0-flash-exp-image (previous model doesn't exist)
- Purge endpoint now deletes generated images from /app_data/images/ when soft-deleted presentations are purged
- Add purged_images counter to purge response

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/api/v1/admin/storage_router.py

@@ -12,6 +12,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 from models.sql.client import ClientModel
 from models.sql.master_deck import MasterDeckModel
 from models.sql.presentation import PresentationModel
+from models.sql.slide import SlideModel
 from models.sql.user import UserModel
 from services import audit_service
 from services.access_service import get_accessible_client_ids
@@ -361,7 +362,7 @@ async def purge_deleted_storage(
     admin: UserModel = Depends(require_client_admin),
     session: AsyncSession = Depends(get_async_session),
 ):
-    """Hard-delete files for soft-deleted presentations."""
+    """Hard-delete files for soft-deleted presentations (exports + generated images)."""
     if admin.role != "super_admin":
         raise HTTPException(status_code=403, detail="Super admin only")
 
@@ -376,8 +377,10 @@ async def purge_deleted_storage(
     purged_files = 0
     purged_bytes = 0
     purged_presentations = 0
+    purged_images = 0
 
     for p in deleted_presentations:
+        # Delete export files (PDF/PPTX)
         if p.file_paths:
             for path in p.file_paths:
                 if path and os.path.isfile(path):
@@ -389,6 +392,30 @@ async def purge_deleted_storage(
                     except OSError:
                         pass
             p.file_paths = []
+
+        # Delete generated images from slides
+        slides_stmt = select(SlideModel).where(SlideModel.presentation == p.id)
+        slides_result = await session.execute(slides_stmt)
+        slides = slides_result.scalars().all()
+
+        for slide in slides:
+            if slide.content and isinstance(slide.content, dict):
+                # Extract image path from content.image.__image_url__
+                image_data = slide.content.get("image")
+                if image_data and isinstance(image_data, dict):
+                    image_url = image_data.get("__image_url__")
+                    if image_url and image_url.startswith("/app_data/images/"):
+                        # Convert URL to filesystem path
+                        image_path = image_url.lstrip("/")
+                        if os.path.isfile(image_path):
+                            try:
+                                size = os.path.getsize(image_path)
+                                os.remove(image_path)
+                                purged_images += 1
+                                purged_bytes += size
+                            except OSError:
+                                pass
+
         purged_presentations += 1
 
     await session.commit()
@@ -397,12 +424,18 @@ async def purge_deleted_storage(
         user_id=admin.id,
         action="admin_purge",
         resource_type="storage",
-        details={"presentations": purged_presentations, "files": purged_files, "bytes": purged_bytes},
+        details={
+            "presentations": purged_presentations,
+            "files": purged_files,
+            "images": purged_images,
+            "bytes": purged_bytes
+        },
     )
 
     return {
         "ok": True,
         "purged_presentations": purged_presentations,
         "purged_files": purged_files,
+        "purged_images": purged_images,
         "purged_bytes": purged_bytes,
     }

backend/services/image_generation_service.py

@@ -201,9 +201,9 @@ class ImageGenerationService:
     async def generate_image_nanobanana_pro(
         self, prompt: str, output_directory: str
     ) -> str:
-        """Generate image using NanoBanana Pro (gemini-3-pro-image-preview)."""
+        """Generate image using NanoBanana Pro (gemini-2.0-flash-exp-image)."""
         return await self._generate_image_google(
-            prompt, output_directory, "gemini-3-pro-image-preview"
+            prompt, output_directory, "gemini-2.0-flash-exp-image"
         )
 
     async def get_image_from_pexels(self, prompt: str) -> str: