fix(frontend): resolve set-state-in-effect lint errors

frontend/src/hooks/useSessionTimer.ts

@@ -11,10 +11,7 @@ export function useSessionTimer(startedAt: string | undefined | null): string |
       intervalRef.current = null
     }
 
-    if (!startedAt) {
-      setElapsed(null)
-      return
-    }
+    if (!startedAt) return
 
     const parsedStartTime = new Date(startedAt).getTime()
     // If the server timestamp is invalid or ahead of the local clock, fall back to "now"
@@ -40,5 +37,5 @@ export function useSessionTimer(startedAt: string | undefined | null): string |
     }
   }, [startedAt])
 
-  return elapsed
+  return startedAt ? elapsed : null
 }