Migrate pre-commit hooks from pre-commit to prek

Replace the Python-based pre-commit framework with prek (Rust) for
faster hook execution. Convert .pre-commit-config.yaml to prek.toml,
remove pre-commit from dev dependencies, and apply ruff auto-fixes
(UP037: remove unnecessary string quotes in type annotations).

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

backend/src/app/models/boss_battle.py

@@ -37,10 +37,10 @@ class BossBattle(Base):
         ForeignKey("games.id"), index=True, default=None
     )
 
-    version_group: Mapped["VersionGroup"] = relationship(back_populates="boss_battles")
-    after_route: Mapped["Route | None"] = relationship()
-    game: Mapped["Game | None"] = relationship()
-    pokemon: Mapped[list["BossPokemon"]] = relationship(
+    version_group: Mapped[VersionGroup] = relationship(back_populates="boss_battles")
+    after_route: Mapped[Route | None] = relationship()
+    game: Mapped[Game | None] = relationship()
+    pokemon: Mapped[list[BossPokemon]] = relationship(
         back_populates="boss_battle", cascade="all, delete-orphan"
     )