Add database overview feature with metrics and UI enhancements

This commit introduces a detailed database overview endpoint and service, providing key metrics such as replication status, database sizes, and performance indicators. On the frontend, a new UI section displays these metrics along with improved forms and troubleshooting tips. Enhancements improve user experience by adding informative tooltips and formatting for byte and time values.

backend/app/api/routes/targets.py

@@ -7,10 +7,12 @@ from app.core.db import get_db
 from app.core.deps import get_current_user, require_roles
 from app.models.models import Metric, QueryStat, Target, User
 from app.schemas.metric import MetricOut, QueryStatOut
+from app.schemas.overview import DatabaseOverviewOut
 from app.schemas.target import TargetCreate, TargetOut, TargetUpdate
 from app.services.audit import write_audit_log
 from app.services.collector import build_target_dsn
 from app.services.crypto import encrypt_secret
+from app.services.overview_service import get_target_overview
 
 router = APIRouter()
 
@@ -179,3 +181,12 @@ async def get_top_queries(target_id: int, user: User = Depends(get_current_user)
         )
         for r in rows
     ]
+
+
+@router.get("/{target_id}/overview", response_model=DatabaseOverviewOut)
+async def get_overview(target_id: int, user: User = Depends(get_current_user), db: AsyncSession = Depends(get_db)) -> DatabaseOverviewOut:
+    _ = user
+    target = await db.scalar(select(Target).where(Target.id == target_id))
+    if not target:
+        raise HTTPException(status_code=404, detail="Target not found")
+    return await get_target_overview(target)