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/schemas/auth/__init__.py

@@ -0,0 +1,7 @@
+from app.schemas.auth.token_pair import TokenPair
+from app.schemas.auth.refresh_request import RefreshRequest
+from app.schemas.auth.token_refreshed import TokenRefreshed
+from app.schemas.auth.logout_request import LogoutRequest
+from app.schemas.auth.register_response import RegisterResponse
+
+__all__ = ["TokenPair", "RefreshRequest", "TokenRefreshed", "LogoutRequest", "RegisterResponse"]

backend/app/schemas/auth/logout_request.py

@@ -0,0 +1,5 @@
+from pydantic import BaseModel
+
+
+class LogoutRequest(BaseModel):
+    refresh_token: str

backend/app/schemas/auth/refresh_request.py

@@ -0,0 +1,5 @@
+from pydantic import BaseModel
+
+
+class RefreshRequest(BaseModel):
+    refresh_token: str

backend/app/schemas/auth/register_response.py

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+from pydantic import BaseModel
+
+from app.schemas.user import UserOut
+
+
+class RegisterResponse(BaseModel):
+    """
+    Returned after registration.
+    Members get tokens immediately (auto-approved).
+    Organizers only get the user object (pending approval).
+    """
+    user: UserOut
+    access_token: str | None = None
+    refresh_token: str | None = None
+    token_type: str = "bearer"

backend/app/schemas/auth/token_pair.py

@@ -0,0 +1,10 @@
+from pydantic import BaseModel
+
+from app.schemas.user import UserOut
+
+
+class TokenPair(BaseModel):
+    access_token: str
+    refresh_token: str
+    token_type: str = "bearer"
+    user: UserOut

backend/app/schemas/auth/token_refreshed.py

@@ -0,0 +1,7 @@
+from pydantic import BaseModel
+
+
+class TokenRefreshed(BaseModel):
+    access_token: str
+    refresh_token: str
+    token_type: str = "bearer"