feat: SAC 0.7.4 sidebar system stats block with UI toggle

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/api/v1/system.py

@@ -0,0 +1,30 @@
+from fastapi import APIRouter, Depends
+from pydantic import BaseModel, Field
+from sqlalchemy.orm import Session
+
+from app.auth.jwt_auth import get_current_user
+from app.database import get_db
+from app.services.system_stats import collect_system_stats
+from app.services.ui_settings import get_effective_ui_settings
+
+router = APIRouter(prefix="/system", tags=["system"])
+
+
+class SystemStatsResponse(BaseModel):
+    visible: bool = Field(description="Показывать блок в боковой панели (глобальная настройка)")
+    collected_at: str
+    cpu_percent: float | None = None
+    memory: dict | None = None
+    disk: dict | None = None
+    database: dict
+    app: dict
+
+
+@router.get("/stats", response_model=SystemStatsResponse)
+def get_system_stats(
+    db: Session = Depends(get_db),
+    _user=Depends(get_current_user),
+) -> SystemStatsResponse:
+    ui = get_effective_ui_settings(db)
+    payload = collect_system_stats(db)
+    return SystemStatsResponse(visible=ui.show_sidebar_system_stats, **payload)