feat(ui): server metrics admin dashboard

Adds /admin/server-metrics page mirroring the Database/ClickHouse visibility
rules: sidebar entry gated on capabilities.infrastructureEndpoints, backend
controller now has @ConditionalOnProperty(infrastructureendpoints) and
class-level @PreAuthorize('hasRole(ADMIN)'). Dashboard panels are driven
from docs/server-self-metrics.md via the generic
/api/v1/admin/server-metrics/{catalog,instances,query} API — Server Health,
JVM, HTTP & DB pools, and conditionally Alerting + Deployments when their
metrics appear in the catalog. ThemedChart / Line / Area from the design
system; hooks in ui/src/api/queries/admin/serverMetrics.ts. Not yet
browser-verified against a running dev server — backend IT covers the API
end-to-end (8 tests), UI typecheck + production bundle both clean.

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

ui/src/components/LayoutShell.tsx

@@ -705,6 +705,7 @@ function LayoutContent() {
         oidc: 'OIDC',
         database: 'Database',
         clickhouse: 'ClickHouse',
+        'server-metrics': 'Server Metrics',
         appconfig: 'App Config',
       };
       const parts = location.pathname.split('/').filter(Boolean);