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/schemas/child.py

@@ -1,5 +1,5 @@
 from datetime import date
-from pydantic import BaseModel
+from pydantic import BaseModel, Field
 
 
 class ChildCreate(BaseModel):
@@ -13,6 +13,7 @@ class ChildUpdate(BaseModel):
     birth_date: date | None = None
     color: str | None = None
     is_active: bool | None = None
+    strikes: int | None = Field(None, ge=0, le=3)
 
 
 class ChildOut(BaseModel):
@@ -21,5 +22,6 @@ class ChildOut(BaseModel):
     birth_date: date | None
     is_active: bool
     color: str
+    strikes: int = 0
 
     model_config = {"from_attributes": True}