feat: add Excel export button to hit parade page

Exports the currently filtered and sorted table (including totals row) to an .xlsx file named with the selected date range. Uses the xlsx library.

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

package.json

@@ -35,6 +35,7 @@
     "react-markdown": "^10.1.0",
     "remark-gfm": "^4.0.1",
     "tailwind-merge": "^3.5.0",
+    "xlsx": "^0.18.5",
     "zod": "^4.3.6",
     "zustand": "^5.0.11"
   },