Implement chain submissions API and update frontend to utilize new endpoint; enhance submissions page with feature flag for API selection, participant progress display, and improved filtering logic.

src/__data__/api/api.ts

@@ -15,6 +15,8 @@ import type {
   UpdateChainRequest,
   SubmitRequest,
   TestSubmissionResult,
+  ChainSubmissionsResponse,
+  SubmissionStatus,
 } from '../../types/challenge'
 
 export const api = createApi({
@@ -143,6 +145,17 @@ export const api = createApi({
       transformResponse: (response: { body: ChallengeSubmission[] }) => response.body,
       providesTags: ['Submission'],
     }),
+    getChainSubmissions: builder.query<
+      ChainSubmissionsResponse,
+      { chainId: string; userId?: string; status?: SubmissionStatus }
+    >({
+      query: ({ chainId, userId, status }) => ({
+        url: `/challenge/chain/${chainId}/submissions`,
+        params: userId || status ? { userId, status } : undefined,
+      }),
+      transformResponse: (response: { body: ChainSubmissionsResponse }) => response.body,
+      providesTags: ['Submission'],
+    }),
 
     // Test submission (LLM check without creating a real submission)
     testSubmission: builder.mutation<TestSubmissionResult, SubmitRequest>({
@@ -178,6 +191,7 @@ export const {
   useGetSystemStatsV2Query,
   useGetUserStatsQuery,
   useGetUserSubmissionsQuery,
+  useGetChainSubmissionsQuery,
   useTestSubmissionMutation,
 } = api