POL-126: Fix critical backend bugs — Championship model/DB mismatch, broken imports

- Restore judges/categories TEXT columns to Championship model (were in DB but missing from model)
- Remove phantom columns not in DB: org_id, subtitle, venue, accent_color
- Remove broken relationships to unmigrated tables (Organization, Discipline, Style, Fee, Rule, Judge)
- Remove broken instagram_service import from lifespan (file doesn't exist)
- Add http://localhost:3000 to default CORS origins (web frontend)

Model files for unmigrated tables kept on disk for future migration.

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

backend/app/models/user.py

@@ -30,7 +30,6 @@ class User(Base):
     refresh_tokens: Mapped[list["RefreshToken"]] = relationship(back_populates="user", cascade="all, delete-orphan")
     registrations: Mapped[list["Registration"]] = relationship(back_populates="user")  # type: ignore[name-defined]
     notification_logs: Mapped[list["NotificationLog"]] = relationship(back_populates="user")  # type: ignore[name-defined]
-    organization: Mapped["Organization | None"] = relationship(back_populates="user", uselist=False)  # type: ignore[name-defined]
 
 
 class RefreshToken(Base):