Add column visibility toggle and drag-sort via settings modal

- Remove default workshop number from search input
- Add ColumnSettingsModal with checkboxes for show/hide per column
- Add drag-and-drop reordering using @dnd-kit/sortable
- Persist column config to localStorage across sessions
- Include search filter, select all/deselect all/reset defaults

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

package.json

@@ -10,6 +10,9 @@
   },
   "dependencies": {
     "@ant-design/icons": "^6.2.5",
+    "@dnd-kit/core": "^6.3.1",
+    "@dnd-kit/sortable": "^10.0.0",
+    "@dnd-kit/utilities": "^3.2.2",
     "antd": "^6.4.3",
     "mssql": "^12.5.5",
     "next": "16.2.9",