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/championship/out.py

@@ -0,0 +1,45 @@
+import json
+import uuid
+from datetime import datetime
+
+from pydantic import BaseModel, model_validator
+
+from app.schemas.organization import OrganizationBrief
+
+
+class ChampionshipOut(BaseModel):
+    model_config = {"from_attributes": True}
+
+    id: uuid.UUID
+    org_id: uuid.UUID | None = None
+    title: str
+    description: str | None
+    location: str | None
+    event_date: datetime | None
+    registration_open_at: datetime | None
+    registration_close_at: datetime | None
+    form_url: str | None
+    entry_fee: float | None
+    video_max_duration: int | None
+    judges: list[dict] | None
+    categories: list[str] | None
+    status: str
+    source: str
+    instagram_media_id: str | None
+    image_url: str | None
+    organization: OrganizationBrief | None = None
+    created_at: datetime
+    updated_at: datetime
+
+    @model_validator(mode="before")
+    @classmethod
+    def parse_json_fields(cls, v):
+        # judges and categories are stored as JSON strings in the DB
+        if hasattr(v, "__dict__"):
+            raw_j = getattr(v, "judges", None)
+            raw_c = getattr(v, "categories", None)
+            if isinstance(raw_j, str):
+                v.__dict__["judges"] = json.loads(raw_j)
+            if isinstance(raw_c, str):
+                v.__dict__["categories"] = json.loads(raw_c)
+        return v