fix(tkfb): 연차 테이블 빈 행 수정 — border/spacing 강제 초기화

- border-collapse/spacing !important 적용
- table-layout: fixed로 컬럼 안정화
- border-top 제거 후 thead 첫 행만 복원

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

system1-factory/web/pages/attendance/annual-overview.html

@@ -63,14 +63,21 @@
     /* 테이블 */
     .data-table {
       width: 100%;
-      border-collapse: collapse;
+      border-collapse: collapse !important;
+      border-spacing: 0 !important;
       font-size: 0.85rem;
       background: white;
+      table-layout: fixed;
     }
+    .data-table thead { display: table-header-group; }
     .data-table th, .data-table td {
       padding: 0.6rem 0.5rem;
       text-align: center;
       border: 1px solid #e5e7eb;
+      border-top: none;
+    }
+    .data-table thead tr:first-child th {
+      border-top: 1px solid #e5e7eb;
     }
     .data-table th {
       background: #f9fafb;