docs: Add APEx Algorithm Dashboard documentation

[Copilot]

Closes the documentation gap for the APEx Algorithm Dashboard — the authenticated admin interface of the Algorithm Catalogue web app — covering capabilities, data sources, access control, and how to request access.

New page: guides/algorithm_catalogue_dashboard.md

• Overview — distinguishes the Dashboard (admin) from the public catalogue; links to source repo
• Key Capabilities — benchmark overview table, scenario drill-down (metrics table + time-series chart), date-range filtering, status badge semantics (healthy / warning / critical / no benchmark), UI layout
• Data & Sources — data types, update cadences, and all four API endpoints (public + admin-only) with link to full API docs in the source repo
• Roles & Permissions — clarifies the two paths to admin access: Keycloak administrator role or institutional e-mail domain listed in the server-side acl-mapping.json allow-list
• Known Limitations — single admin role, no bulk export UI, no comparison view, benchmark-only metrics, cost figures are estimates
• Requesting Access — step-by-step instructions via a GitHub issue; fields required; note that the issue is public so sensitive data (e-mail) should not be included; 5-business-day turnaround; approval criteria

Sidebar: _quarto.yml

Adds the new page as a third entry under the existing APEx Algorithm Catalogue developer guide section, alongside the existing "Registering your service" and "Creating benchmarks" pages.