Add new API endpoint for retrieving submissions by challenge chain; update frontend to support chain selection and display participant progress. Enhance localization for submissions page in English and Russian.

locales/en.json

@@ -166,8 +166,21 @@
   "challenge.admin.submissions.title": "Solution attempts",
   "challenge.admin.submissions.loading": "Loading attempts...",
   "challenge.admin.submissions.load.error": "Failed to load attempts list",
+  "challenge.admin.submissions.select.chain": "Select a chain to view participant attempts",
+  "challenge.admin.submissions.chain.tasks": "tasks",
+  "challenge.admin.submissions.chain.click": "Click to view attempts",
+  "challenge.admin.submissions.no.chains.title": "No chains",
+  "challenge.admin.submissions.no.chains.description": "Create a task chain to get started",
+  "challenge.admin.submissions.back.to.chains": "Back to chain selection",
+  "challenge.admin.submissions.chain.description": "Total tasks in chain: {{count}}",
+  "challenge.admin.submissions.participants.title": "Chain participants",
+  "challenge.admin.submissions.participants.description": "Select a participant to view their attempts in this chain",
+  "challenge.admin.submissions.participants.empty.title": "No participants",
+  "challenge.admin.submissions.participants.empty.description": "No one has submitted solutions in this chain yet",
+  "challenge.admin.submissions.participants.click.to.view": "→ view",
   "challenge.admin.submissions.search.placeholder": "Search by user or task...",
   "challenge.admin.submissions.filter.user": "Select user",
+  "challenge.admin.submissions.filter.user.clear": "← All participants",
   "challenge.admin.submissions.filter.status": "Status",
   "challenge.admin.submissions.status.all": "All statuses",
   "challenge.admin.submissions.status.accepted": "Accepted",