feat(metrics): Implement dashboard metrics API and integrate metrics chart components

backend/app/schemas/__init__.py

@@ -1,6 +1,7 @@
 from app.schemas.activity_events import ActivityEventRead
 from app.schemas.agents import AgentCreate, AgentRead, AgentUpdate
 from app.schemas.boards import BoardCreate, BoardRead, BoardUpdate
+from app.schemas.metrics import DashboardMetrics
 from app.schemas.tasks import TaskCreate, TaskRead, TaskUpdate
 from app.schemas.users import UserCreate, UserRead, UserUpdate
 
@@ -12,6 +13,7 @@ __all__ = [
     "BoardCreate",
     "BoardRead",
     "BoardUpdate",
+    "DashboardMetrics",
     "TaskCreate",
     "TaskRead",
     "TaskUpdate",