Fix blank labels on shared reports grouped by date intervals

[1yakub]

What does this PR do?

• Fixes Shared report shows blank names when the report is grouped by day, week, month or year #1200

Shared report links grouped by day, week, month or year rendered without labels: the table rows and pie chart segments had no name and the Group by heading was blank. The backend leaves description null for date interval groups (loadDescriptorsMap has no branch for them) and the page fell back to emptyPlaceholder, which has no date entries either. The chart at the top was the only labeled part because it formats el.key itself.

This resolves date group names on the shared report page from entry.key, with the same formatWeek and formatDate helpers that ReportingChart.vue already uses and the date_format the report payload already carries. Entity groupings keep the existing description and placeholder behavior.

The thinking behind the decisions:

• Fixed in the frontend instead of filling description in the backend, so the labels respect the organization date format the payload sends and stay consistent with how the chart right above the table formats the same keys.
• The pie chart's gray bucket now keys on entry.key === null instead of entry.description === null, because date groups have a null description but a real key. The none bucket stays gray, date slices get their formatted name and a seeded color.
• getGroupLabel falls back to the raw value, so the heading cannot render blank for an unknown group type.
• Week keys come out exactly as the chart already shows them ("Week 31"). Day, month and year keys go through formatDate like the chart axis does.

What I tested and how

• npm run format:check, npm run lint (0 errors) and npm run test:unit (185 passing) locally.
• npm run type-check reports no issues in the changed file. The only error in my environment is the pre existing vendor/tightenco/ziggy resolution in app.ts, which needs a composer install and is unrelated to this change.
• Checked in the API client schema that DetailedWithDataReportResource includes key on both grouping levels, so the public payload already carries everything the page needs.
• I did not run a full backend to view the page live. If you want an e2e case for this I am happy to extend e2e/shared-reports.spec.ts with a report grouped by week created through the API.

Checklist (DO NOT REMOVE)

• I read the contributing guide
• I signed the Contributor License Agreement.
• I commented my code, particularly in hard-to-understand areas

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