docs(agents): document stale Helm subchart cleanup (#1957)

Refs: #1947

Signed-off-by: Evan Lezar <elezar@nvidia.com>

.agents/skills/helm-dev-environment/SKILL.md

@@ -212,6 +212,33 @@ mise run helm:k3s:status
 
 ---
 
+## Helm Chart Checks
+
+Run the chart lint task before changing Helm templates, values overlays, or
+Skaffold inputs:
+
+```bash
+mise run helm:lint
+```
+
+If Helm reports missing chart dependencies, remove the specific stale subchart
+archive or directory named by the error from `deploy/helm/openshell/charts/`,
+then rerun the lint task.
+
+For example, when lint reports `chart metadata is missing these dependencies:
+postgresql`, remove stale PostgreSQL chart artifacts:
+
+```bash
+rm -f deploy/helm/openshell/charts/postgresql-*.tgz
+rm -rf deploy/helm/openshell/charts/postgresql
+mise run helm:lint
+```
+
+The `charts/` directory is ignored and regenerated by `helm dependency build`
+for dependencies still declared in `Chart.yaml`.
+
+---
+
 ## Key Files
 
 | Path | Purpose |