feat(ansible): standardize Neo4j ports and add monitoring

- Unify Neo4j HTTP/Bolt/syslog ports across ariel and umbriel hosts
- Add neo4j_metrics_port (22094) for APOC exporter sidecar
- Add umbriel to Prometheus node_exporter targets
- Add Neo4j scrape config and alerts for tx rollback rate and
  stalled store growth
- Replace kernos_harper MCP with andromeda (caliban.helu.ca)
- Remove angelia MCP from kottos fastagent config
- Switch neo4j group membership from keeper_user to ponos

ansible/kottos/fastagent.config.yaml.j2

@@ -54,17 +54,11 @@ mcp:
       url: "{{ kottos_grafana_url | default('http://miranda.incus:25533/mcp') }}"
 
     # ── Shell + file operations — Kernos (Korax) ─────────────────────────────
-    kernos_harper:
+    andromeda:
       transport: http
-      url: "{{ kottos_kernos_harper_url | default('http://korax.helu.ca:20261/mcp') }}"
+      url: "{{ kottos_kernos_harper_url | default('http://caliban.helu.ca:20261/mcp') }}"
       load_on_start: false
 
-    # ── Angelia messaging ───────────────────────────────────────────────────
-    # Auth header provided by fastagent.secrets.yaml (vault-rendered).
-    angelia:
-      transport: http
-      url: "{{ kottos_angelia_url | default('https://ouranos.helu.ca/mcp/') }}"
-
     # ── GitHub MCP Server (local Docker, stdio) ──────────────────────────────
     # GITHUB_PERSONAL_ACCESS_TOKEN provided by fastagent.secrets.yaml
     github: