Move 3 Strikes from Admin to Dashboard, add strikes feature

- Adds strikes (0-3) to Child model with migration
- New PATCH /api/children/{id}/strikes endpoint with WebSocket broadcast
- TV dashboard shows red ✕ marks next to child name when strikes > 0
- 3 Strikes card on Dashboard page (removed from Admin)

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

backend/app/routers/children.py

@@ -1,4 +1,5 @@
 from fastapi import APIRouter, Depends, HTTPException, status
+from pydantic import BaseModel, Field
 from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy import select
 
@@ -6,6 +7,7 @@ from app.dependencies import get_db, get_current_user
 from app.models.child import Child
 from app.models.user import User
 from app.schemas.child import ChildCreate, ChildOut, ChildUpdate
+from app.websocket.manager import manager
 
 router = APIRouter(prefix="/api/children", tags=["children"])
 
@@ -70,6 +72,30 @@ async def update_child(
     return child
 
 
+class StrikesBody(BaseModel):
+    strikes: int = Field(..., ge=0, le=3)
+
+
+@router.patch("/{child_id}/strikes", response_model=ChildOut)
+async def update_strikes(
+    child_id: int,
+    body: StrikesBody,
+    current_user: User = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    result = await db.execute(
+        select(Child).where(Child.id == child_id, Child.user_id == current_user.id)
+    )
+    child = result.scalar_one_or_none()
+    if not child:
+        raise HTTPException(status_code=404, detail="Child not found")
+    child.strikes = body.strikes
+    await db.commit()
+    await db.refresh(child)
+    await manager.broadcast(child_id, {"event": "strikes_update", "strikes": child.strikes})
+    return child
+
+
 @router.delete("/{child_id}", status_code=status.HTTP_204_NO_CONTENT)
 async def delete_child(
     child_id: int,