chore: ship slice #34 — dashboardAPI walking skeleton + Grafana pin

- Bumps nodes/dashboardAPI submodule to slice/34-walking-skeleton@7fdab73
  (credentials block for bearer token, folderUid config field, basic tests).
- Pins grafana/grafana to 11.3.0 — legacy /api/dashboards/db is the
  generator target; G12 K8s-style API is out of scope (PRD constraint).

Refs #34

docker-compose.yml

@@ -67,7 +67,10 @@ services:
   # Grafana — dashboard visualization
   # ---------------------------------------------------------
   grafana:
-    image: grafana/grafana:latest
+    # Pinned per dashboardAPI v2 PRD: legacy POST /api/dashboards/db is the
+    # generator target; Grafana 12 K8s-style API is out of scope. Bump
+    # deliberately, not via `pull --latest`.
+    image: grafana/grafana:11.3.0
     container_name: evolv-grafana
     restart: unless-stopped
     ports: