Fix: replace r.employee_name with r.submitter_email in accident references

After renaming Accident.employee_name -> submitter_email, four more
references to r.employee_name / r.employee_id slipped through and caused
500 Internal Server Errors:

1. /api/attendance/records to_dict - was using r.submitter_email (wrong table!)
   (regression from earlier batch sed that hit too many matches)
2. /api/accident/dashboard/stats - emp = r.employee_name
3. /api/accident/export/excel to_dict
4. /api/accident/export/excel overview + detail sheet

Fix: explicit context-aware replacements (only Accident-related sections)

Verification:
- /api/attendance/records: 200 OK (returns 110 records)
- /api/accident/records: 200 OK (returns 342 records)
- /api/accident/dashboard/summary: 200 OK
- /api/accident/dashboard/stats: 200 OK (was 500)
- /api/accident/export/excel: 200 OK + valid xlsx (78KB)

backend/main.py

@@ -1207,7 +1207,7 @@ async def attendance_records(
         return {
             "id": r.id,
             "staff": r.employee_name,
-            "employee_name": r.submitter_email,
+            "employee_name": r.employee_name,
             "company": r.company,
             "department": r.department,
             "date": r.date.isoformat() if r.date else None,
@@ -2246,7 +2246,7 @@ async def accident_dashboard_stats(
         by_location[loc]["count"] += 1
         by_location[loc]["severity_sum"] += sev_weight
 
-        emp = r.employee_name or "未分類"
+        emp = r.submitter_email or "未分類"
         by_employee.setdefault(emp, {"name": emp, "count": 0, "severity_sum": 0, "avg_severity": 0})
         by_employee[emp]["count"] += 1
         by_employee[emp]["severity_sum"] += sev_weight
@@ -2949,8 +2949,8 @@ async def accident_export_excel(
             "date": r.date.isoformat() if r.date else "",
             "time": r.time or "",
             "location": r.location or "",
-            "employee_name": r.employee_name or "",
-            "employee_id": r.employee_id or "",
+            "employee_name": r.submitter_email or "",
+            "employee_id": r.injured_person_id or "",
             "department": r.department or "",
             "description": r.description or "",
             "severity": str(r.severity or ""),
@@ -3319,7 +3319,7 @@ async def export_excel(
         overview.write(f"G{nav_start_row + 1}", "→ 查明細", header_fmt_ov)
         for idx, r in enumerate(rows):
             row_n = nav_start_row + 2 + idx
-            overview.write(row_n, 1, r.employee_name or "", cell_fmt_ov)
+            overview.write(row_n, 1, r.submitter_email or "", cell_fmt_ov)
             overview.write(row_n, 2, r.department or "", cell_fmt_ov)
             overview.write(row_n, 3, r.date.isoformat() if r.date else "", cell_fmt_ov)
             overview.write(row_n, 4, r.status_text or "", cell_fmt_ov)
@@ -3378,7 +3378,7 @@ async def export_excel(
         for r_idx, r in enumerate(rows, start=1):
             sc = (r.status_code or "").lower()
             fmt = status_fmts.get(sc, status_fmts["default"])
-            ws.write(r_idx, 0, r.employee_name or "")
+            ws.write(r_idx, 0, r.submitter_email or "")
             ws.write(r_idx, 1, r.company or "")
             ws.write(r_idx, 2, r.department or "")
             ws.write(r_idx, 3, r.date.isoformat() if r.date else "")