Scope dashboard REST endpoint: return linked dashboard + panels (each panel executes with scope_id)

GET /resource/scopes/{scope_type}/{scope_id}/dashboard. Return the dashboard linked to the scope plus its panels; each panel's preset executes with scope_id as id. Web UI renders natively (descriptors + values). Gate on the scoped read-permission check.

Success Criteria:
- [ ] Returns the linked dashboard + ordered panels with executed values for a scope with a link.
- [ ] Scope with no linked dashboard -> empty/404 per contract.
- [ ] Each panel value reflects scope_id-bound preset execution.
- [ ] Unauthorized requester -> 403.
- [ ] pants test passes for affected packages

JIRA Issue: BA-6756

Start by locating the GET /resource/scopes/{scope_type}/{scope_id}/dashboard route and the code that loads linked dashboards, panels, and presets. Trace the scoped read-permission check, then run the affected packages with pants test; done means the success criteria pass, including the no-dashboard response contract and 403 handling.

Written by the indexing model from the issue text.