feat(infra): remove Go dashboard, dashboard is now part of hub Next.js app

- Remove dashboard container from observability.yml
- Remove infra/docker/dashboard.Dockerfile
- Remove dashboard route from Traefik apps.yaml
- Mount Docker socket on hub container for /api/dashboard
- Remove dashboard build from CI/CD (docker-build-push.yml)
- Update submodule pointer to hub with Next.js dashboard rewrite

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

infra/compose/hub.yml

@@ -9,6 +9,8 @@ services:
           - hub
     env_file:
       - ../../.env
+    volumes:
+      - /var/run/docker.sock:/var/run/docker.sock:ro
 
 networks:
   app-shared-net:

infra/compose/observability.yml

@@ -73,28 +73,6 @@ services:
     volumes:
       - /:/host:ro,rslave
 
-  # ── Custom Dashboard (nginx:alpine) ──
-  dashboard:
-    container_name: dashboard
-    image: ghcr.io/asepharyana/asepharyana-hub/dashboard:sha-5999ac1
-    build:
-      context: ../..
-      dockerfile: infra/docker/dashboard.Dockerfile
-    restart: always
-    networks:
-      app-shared-net:
-        aliases:
-          - dashboard
-    ports:
-      - '8080:8080'
-    volumes:
-      - /var/run/docker.sock:/var/run/docker.sock:ro
-    depends_on:
-      jaeger:
-        condition: service_started
-      otel-collector:
-        condition: service_started
-
 networks:
   app-shared-net:
     name: app-shared-net