POL-127: Add organizations table and championship ownership

- Create organizations table with Alembic migration (3-phase: create table, migrate data, drop old column)
- Add org_id FK on championships linking to organizations
- Refactor all schemas into one-class-per-file packages (auth, championship, organization, participant, registration, user)
- Update CRUD layer with selectinload for organization relationships
- Update frontend types and components to use nested organization object
- Remove phantom Championship fields (subtitle, venue, accent_color) from frontend

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

backend/app/crud/crud_championship.py

@@ -3,6 +3,7 @@ import uuid
 
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy.orm import selectinload
 
 from app.models.championship import Championship
 from app.schemas.championship import ChampionshipCreate, ChampionshipUpdate
@@ -16,7 +17,9 @@ def _serialize(value) -> str | None:
 
 async def get(db: AsyncSession, champ_id: str | uuid.UUID) -> Championship | None:
     cid = champ_id if isinstance(champ_id, uuid.UUID) else uuid.UUID(str(champ_id))
-    result = await db.execute(select(Championship).where(Championship.id == cid))
+    result = await db.execute(
+        select(Championship).where(Championship.id == cid).options(selectinload(Championship.organization))
+    )
     return result.scalar_one_or_none()
 
 
@@ -26,7 +29,7 @@ async def list_all(
     skip: int = 0,
     limit: int = 50,
 ) -> list[Championship]:
-    q = select(Championship).order_by(Championship.event_date.asc())
+    q = select(Championship).order_by(Championship.event_date.asc()).options(selectinload(Championship.organization))
     if status:
         q = q.where(Championship.status == status)
     q = q.offset(skip).limit(limit)
@@ -34,14 +37,16 @@ async def list_all(
     return list(result.scalars().all())
 
 
-async def create(db: AsyncSession, data: ChampionshipCreate) -> Championship:
+async def create(db: AsyncSession, data: ChampionshipCreate, org_id: uuid.UUID | None = None) -> Championship:
     payload = data.model_dump(exclude={"judges", "categories"})
     payload["judges"] = _serialize(data.judges)
     payload["categories"] = _serialize(data.categories)
+    if org_id:
+        payload["org_id"] = org_id
     champ = Championship(**payload)
     db.add(champ)
     await db.commit()
-    await db.refresh(champ)
+    await db.refresh(champ, attribute_names=["organization"])
     return champ