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/user/__init__.py

@@ -0,0 +1,6 @@
+from app.schemas.user.register import UserRegister
+from app.schemas.user.login import UserLogin
+from app.schemas.user.out import UserOut
+from app.schemas.user.update import UserUpdate
+
+__all__ = ["UserRegister", "UserLogin", "UserOut", "UserUpdate"]

backend/app/schemas/user/login.py

@@ -0,0 +1,6 @@
+from pydantic import BaseModel, EmailStr
+
+
+class UserLogin(BaseModel):
+    email: EmailStr
+    password: str

backend/app/schemas/user/out.py

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+import uuid
+from datetime import datetime
+
+from pydantic import BaseModel
+
+from app.schemas.organization import OrganizationOut
+
+
+class UserOut(BaseModel):
+    model_config = {"from_attributes": True}
+
+    id: uuid.UUID
+    email: str
+    full_name: str
+    phone: str | None
+    role: str
+    status: str
+    instagram_handle: str | None
+    organization: OrganizationOut | None = None
+    expo_push_token: str | None
+    created_at: datetime

backend/app/schemas/user/register.py

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+from typing import Literal
+
+from pydantic import BaseModel, EmailStr, field_validator
+
+
+class UserRegister(BaseModel):
+    email: EmailStr
+    password: str
+    full_name: str
+    phone: str | None = None
+    # Role requested at registration: 'member' or 'organizer'
+    requested_role: Literal["member", "organizer"] = "member"
+    # Organizer-only fields
+    organization_name: str | None = None
+    instagram_handle: str | None = None
+
+    @field_validator("organization_name")
+    @classmethod
+    def org_name_required_for_organizer(cls, v, info):
+        if info.data.get("requested_role") == "organizer" and not v:
+            raise ValueError("Organization name is required for organizer registration")
+        return v

backend/app/schemas/user/update.py

@@ -0,0 +1,10 @@
+from pydantic import BaseModel
+
+
+class UserUpdate(BaseModel):
+    full_name: str | None = None
+    phone: str | None = None
+    instagram_handle: str | None = None
+    expo_push_token: str | None = None
+    # Org fields — routed to Organization table in CRUD
+    organization_name: str | None = None