fix(admin): show username in submissions and add testcase links to problems list

Submissions list and detail pages now display the username alongside the
user ID instead of showing only a numeric ID. The problems list page now
includes a direct link to each problem's testcases for easier navigation.

https://claude.ai/code/session_01JF5ZmGAQ4zNbhV5DM729Fw

1 files changed, 8 insertions, 0 deletions

diff --git a/backend/admin/handler_test.go b/backend/admin/handler_test.go
index 994c584..f340fef 100644
--- a/backend/admin/handler_test.go
+++ b/backend/admin/handler_test.go
@@ -1182,6 +1182,11 @@ func TestGetSubmissions_Success(t *testing.T) {
 				},
 			}, nil
 		},
+		listUsersFunc: func(_ context.Context) ([]db.User, error) {
+			return []db.User{
+				{UserID: 1, Username: "alice"},
+			}, nil
+		},
 	}
 	h := newTestHandler(q)
 
@@ -1208,6 +1213,9 @@ func TestGetSubmissionDetail_Success(t *testing.T) {
 				CreatedAt:    pgtype.Timestamp{Valid: true},
 			}, nil
 		},
+		getUserByIDFunc: func(_ context.Context, userID int32) (db.User, error) {
+			return db.User{UserID: userID, Username: "alice"}, nil
+		},
 		getTestcaseResultsBySubmIDFunc: func(_ context.Context, _ int32) ([]db.TestcaseResult, error) {
 			return []db.TestcaseResult{
 				{