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/main.py

@@ -1,5 +1,3 @@
-from contextlib import asynccontextmanager
-
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 
@@ -7,19 +5,7 @@ from app.config import settings
 from app.routers import auth, championships, registrations, participant_lists, users
 
 
-@asynccontextmanager
-async def lifespan(app: FastAPI):
-    # Start Instagram sync scheduler if configured
-    if settings.INSTAGRAM_USER_ID and settings.INSTAGRAM_ACCESS_TOKEN:
-        from app.services.instagram_service import start_scheduler
-        scheduler = start_scheduler()
-        yield
-        scheduler.shutdown()
-    else:
-        yield
-
-
-app = FastAPI(title="Pole Dance Championships API", version="1.0.0", lifespan=lifespan)
+app = FastAPI(title="Pole Dance Championships API", version="1.0.0")
 
 app.add_middleware(
     CORSMiddleware,