feat(admin): apix-admin UI at admin.api-index.org

Internal maintainer dashboard: global stats, sandbox list with
tier-filter and pagination, sandbox drill-down with D3 world map,
tier-promotion form. API-key auth via HttpOnly cookie. Port 8084,
rolling a/b deploy alongside the existing service pairs.

- apix-common: AdminSandboxSummary, AdminSandboxListResponse, AdminStatsResponse DTOs
- apix-registry: AdminResource (4 endpoints), SandboxService.listAllSandboxes + getGlobalStats
- apix-registry: SandboxResource GET /{uuid}/dashboard endpoint (was missing — fixes portal 500)
- apix-portal: RegistryClient path corrected to /dashboard
- apix-admin: new Quarkus module — auth filter, registry REST client, 3 resources, 6 Qute templates, admin.js
- infra: Dockerfile.admin, docker-compose admin-a/b services, Caddyfile admin.api-index.org block
- scripts: deploy-bluegreen.sh extended for admin-a/b

Co-Authored-By: Mira Rehfeld <noreply@anthropic.com>

infra/docker-compose.yml

@@ -173,6 +173,38 @@ services:
       retries: 3
     restart: unless-stopped
 
+  # ── Admin UI (a/b) ────────────────────────────────────────────────────────
+
+  admin-a:
+    image: apix-admin:latest
+    environment:
+      APIX_REGISTRY_URL: http://registry-a:8180
+      APIX_API_KEY: ${APIX_API_KEY}
+      LOG_LEVEL: ${LOG_LEVEL:-INFO}
+    depends_on:
+      - registry-a
+    healthcheck:
+      test: ["CMD-SHELL", "wget -qO- http://localhost:8084/q/health/live || exit 1"]
+      interval: 30s
+      timeout: 10s
+      retries: 3
+    restart: unless-stopped
+
+  admin-b:
+    image: apix-admin:latest
+    environment:
+      APIX_REGISTRY_URL: http://registry-b:8180
+      APIX_API_KEY: ${APIX_API_KEY}
+      LOG_LEVEL: ${LOG_LEVEL:-INFO}
+    depends_on:
+      - registry-b
+    healthcheck:
+      test: ["CMD-SHELL", "wget -qO- http://localhost:8084/q/health/live || exit 1"]
+      interval: 30s
+      timeout: 10s
+      retries: 3
+    restart: unless-stopped
+
   # ── Edge proxy ────────────────────────────────────────────────────────────
 
   caddy: