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/config.py

@@ -18,7 +18,7 @@ class Settings(BaseSettings):
 
     EXPO_ACCESS_TOKEN: str = ""
 
-    CORS_ORIGINS: str = "http://localhost:8081,exp://"
+    CORS_ORIGINS: str = "http://localhost:3000,http://localhost:8081,exp://"
 
     @property
     def cors_origins_list(self) -> list[str]: