Dashboard/panel/link admin write management (create/update/delete/purge; no read op)

Write-only v2 slice for dashboards, panels, and scope links (create/update/delete/purge), mirroring the preset write path. Panel ordering editable; scope-link create/remove. Do NOT add get/search (read) ops - dashboard read is served by the scope dashboard endpoint plus the scoped permission check.

Success Criteria:
- [ ] create dashboard + add panels (ordered) -> persisted (read verified via the scope dashboard endpoint).
- [ ] link/unlink a scope_type to a dashboard.
- [ ] delete dashboard removes/blocks its panels per FK policy.
- [ ] No separate read (get/search) op added.
- [ ] Non-admin denied.
- [ ] pants test passes for affected packages

JIRA Issue: BA-6754

Start by tracing the existing preset write path and the scope dashboard endpoint mentioned in the issue. Identify the affected packages and run the relevant Pants tests before implementing dashboard, panel-ordering, and scope-link write behavior. Done means persistence and deletion behavior meet the listed criteria, non-admin writes are denied, no read operation is added, and affected-package tests pass.

Written by the indexing model from the issue text.