Adds a Datenexport action button at the end of the project-detail tabs
nav. Hidden by default; revealed when canExportProject() returns true
(global_admin OR direct team responsibility ∈ {lead, member}) — mirror
of the server-side §4 gate. Server re-enforces on the request.
Click handler swaps in a transient <a download> that hits
GET /api/projects/{id}/export — browser handles the download via
Content-Disposition. Same pattern as the personal export in
client/settings.ts.
4 new i18n keys (DE+EN):
- projects.detail.tab.export (n/a — uses .export.button on the action)
- projects.detail.export.button = "Daten exportieren" / "Export data"
- projects.detail.export.tooltip with hint about subtree inclusion
Total i18n keys now 2479.