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/__init__.py

@@ -1,26 +1,14 @@
 from app.models.user import User, RefreshToken
-from app.models.organization import Organization
 from app.models.championship import Championship
 from app.models.registration import Registration
 from app.models.participant import ParticipantList
 from app.models.notification import NotificationLog
-from app.models.discipline import Discipline
-from app.models.style import Style
-from app.models.fee import Fee
-from app.models.rule import Rule
-from app.models.judge import Judge
 
 __all__ = [
     "User",
     "RefreshToken",
-    "Organization",
     "Championship",
     "Registration",
     "ParticipantList",
     "NotificationLog",
-    "Discipline",
-    "Style",
-    "Fee",
-    "Rule",
-    "Judge",
 ]