Add department-level monthly storage report email with PDF attachment

[claire-peters]

Summary

• Add dept_storage_report.txt email template with department name, ticket address, and signature variables
• Add DepartmentStorageReportView (PDFView) in department/views.py gated to superusers and department approvers, rendering a usage summary card and monthly storage invoice details table (matching the DepartmentDetail page, without pagination)
• Add <int:pk>/report URL route (department-report) in department/urls.py
• Add send_dept_storage_report_emails() and send_dept_storagereport_pdf() to project/tasks.py — sends to departments with rank school or institution, addressed to members with the Approver role

Test plan

• Navigate to /department/<pk>/report as a superuser and confirm PDF renders with usage summary and invoice details table
• Navigate to /department/<pk>/report as a department Approver and confirm access is granted
• Navigate to /department/<pk>/report as a non-member and confirm 403
• Confirm usage summary counts (labs, allocations, users) only reflect labs with active storage allocations
• Call send_dept_storage_report_emails() in the Django shell and confirm emails are sent only for departments with rank school or institution
• Confirm departments with other ranks are skipped
• Confirm PDF attachment is named <DeptCode>_<Month>_<Year>_dept_storagereport.pdf