Separate PokeAPI ID from national dex for correct form identification

Pokemon forms (e.g., Alolan Rattata) had their PokeAPI ID (10091) stored as
national_dex, causing them to display incorrectly. This renames the unique
identifier to pokeapi_id and adds a real national_dex field shared between
forms and their base species, so Alolan Rattata correctly shows as #19.

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

backend/src/app/models/pokemon.py

@@ -1,4 +1,4 @@
-from sqlalchemy import SmallInteger, String
+from sqlalchemy import Integer, SmallInteger, String
 from sqlalchemy.dialects.postgresql import ARRAY
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
@@ -9,7 +9,8 @@ class Pokemon(Base):
     __tablename__ = "pokemon"
 
     id: Mapped[int] = mapped_column(primary_key=True)
-    national_dex: Mapped[int] = mapped_column(SmallInteger, unique=True)
+    pokeapi_id: Mapped[int] = mapped_column(Integer, unique=True)
+    national_dex: Mapped[int] = mapped_column(SmallInteger)
     name: Mapped[str] = mapped_column(String(50))
     types: Mapped[list[str]] = mapped_column(ARRAY(String(20)))
     sprite_url: Mapped[str | None] = mapped_column(String(500))
@@ -22,4 +23,4 @@ class Pokemon(Base):
     )
 
     def __repr__(self) -> str:
-        return f"<Pokemon(id={self.id}, name='{self.name}', dex={self.national_dex})>"
+        return f"<Pokemon(id={self.id}, name='{self.name}', pokeapi_id={self.pokeapi_id}, dex={self.national_dex})>"