Apply technical-light design system to the gateway dashboard

Restyles the Blazor dashboard onto a portable token-based theme so it
reads like an instrument panel: warm-paper background, hairline-ruled
panels, IBM Plex type, monospace tabular numerics, and status carried by
colour chips. Vendors theme.css + IBM Plex fonts, rewrites dashboard.css
as a thin token-driven view layer, and swaps the Bootstrap navbar and
status badges for the design-system app bar and chips.

Also includes pending API-key management, Galaxy hierarchy projection,
and constraint-enforcement work with their tests.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/MxGateway.Server/Dashboard/DashboardApiKeyManagementRequest.cs

@@ -0,0 +1,9 @@
+using MxGateway.Server.Security.Authentication;
+
+namespace MxGateway.Server.Dashboard;
+
+public sealed record DashboardApiKeyManagementRequest(
+    string KeyId,
+    string DisplayName,
+    IReadOnlySet<string> Scopes,
+    ApiKeyConstraints Constraints);