feat: Add pagination with total count to generation listings and enable filtering assets by type.

repos/generation_repo.py

@@ -39,5 +39,13 @@ class GenerationRepo:
             generations.append(Generation(**generation))
         return generations
 
+    async def count_generations(self, character_id: Optional[str] = None, status: Optional[GenerationStatus] = None) -> int:
+        args = {}
+        if character_id is not None:
+            args["linked_character_id"] = character_id
+        if status is not None:
+            args["status"] = status
+        return await self.collection.count_documents(args)
+
     async def update_generation(self, generation: Generation, ):
         res = await self.collection.update_one({"_id": ObjectId(generation.id)}, {"$set": generation.model_dump()})