[OPIK-5758] [FE] fix: persist eval suite experiment state across page refresh (#6158)

Remove experimentByPromptId from the localStorage exclusion list so the
prompt-to-experiment mapping survives page refresh, aligning eval suite
persistence with regular dataset playground runs.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: itamargolan

apps/opik-frontend/src/store/PlaygroundStore.ts

@@ -445,7 +445,6 @@ const usePlaygroundStore = create<PlaygroundStore>()(
           progressPhase,
           progressTotal,
           progressCompleted,
-          experimentByPromptId,
           isRunning,
           isRunningMap,
           ...rest