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/seed.py

@@ -1,4 +1,4 @@
-"""Seed script — creates test users and one championship.
+"""Seed script — creates test users, organization, and championships.
 Run from backend/: .venv/Scripts/python seed.py
 """
 import asyncio
@@ -7,6 +7,7 @@ from datetime import UTC, datetime, timedelta
 
 from app.database import AsyncSessionLocal
 from app.models.championship import Championship
+from app.models.organization import Organization
 from app.models.user import User
 from app.services.auth_service import hash_password
 from sqlalchemy import select
@@ -29,6 +30,7 @@ async def seed():
                 "password": "Org1234",
                 "role": "organizer",
                 "status": "approved",
+                "instagram_handle": "@ekaterina_pole",
             },
             {
                 "email": "member@pole.dev",
@@ -36,6 +38,7 @@ async def seed():
                 "password": "Member1234",
                 "role": "member",
                 "status": "approved",
+                "instagram_handle": "@anna_petrova",
             },
             {
                 "email": "pending@pole.dev",
@@ -57,11 +60,11 @@ async def seed():
                     full_name=ud["full_name"],
                     role=ud["role"],
                     status=ud["status"],
+                    instagram_handle=ud.get("instagram_handle"),
                 )
                 db.add(user)
                 print(f"  Created user: {ud['email']}")
             else:
-                # Update role/status if needed
                 user.role = ud["role"]
                 user.status = ud["status"]
                 user.hashed_password = hash_password(ud["password"])
@@ -70,6 +73,27 @@ async def seed():
 
         await db.flush()
 
+        # ── Organization ──────────────────────────────────────────────────────
+        organizer = created_users["organizer@pole.dev"]
+        result = await db.execute(select(Organization).where(Organization.user_id == organizer.id))
+        org = result.scalar_one_or_none()
+        if org is None:
+            org = Organization(
+                user_id=organizer.id,
+                name="Pole Studio Minsk",
+                instagram="@polestudio_minsk",
+                email="organizer@pole.dev",
+                city="Minsk",
+                verified=True,
+                status="active",
+            )
+            db.add(org)
+            print(f"  Created organization: {org.name}")
+        else:
+            print(f"  Organization already exists: {org.name}")
+
+        await db.flush()
+
         # ── Championships ──────────────────────────────────────────────────────
         championships_data = [
             {
@@ -115,11 +139,12 @@ async def seed():
             )
             champ = result.scalar_one_or_none()
             if champ is None:
-                champ = Championship(**cd)
+                champ = Championship(org_id=org.id, **cd)
                 db.add(champ)
                 print(f"  Created championship: {cd['title']}")
             else:
-                print(f"  Championship already exists: {cd['title']}")
+                champ.org_id = org.id
+                print(f"  Updated championship: {cd['title']}")
 
         await db.commit()
         print("\nSeed complete!")