Restructure into full project layout

backend/app/schemas/collection.py

@@ -0,0 +1,29 @@
+from pydantic import BaseModel
+
+
+class CollectionCardOut(BaseModel):
+    id: int
+    card_name: str
+    set_code: str
+    collector_number: str
+    quantity: int
+    foil_quantity: int
+    scryfall_id: str
+    scryfall_data: dict | None
+
+    model_config = {"from_attributes": True}
+
+
+class CollectionStatsOut(BaseModel):
+    total_cards: int
+    unique_cards: int
+    foil_cards: int
+    estimated_value: float | None
+
+
+class PaginatedCollection(BaseModel):
+    items: list[CollectionCardOut]
+    total: int
+    page: int
+    page_size: int
+    pages: int