fix(helm): build chart dependencies before lint

[elezar]

Summary

Build Helm chart dependencies before running chart lint and helm-unittest so optional subchart dependencies are resolved consistently.

Related Issue

None.

Changes

• Run helm dependency build deploy/helm/openshell before helm lint.
• Run helm dependency build deploy/helm/openshell before helm unittest.

Testing

• mise run pre-commit passes
• mise run helm:lint passes
• mise run helm:test passes
• Unit tests added/updated
• E2E tests added/updated (if applicable)

Note: mise run pre-commit was run and failed in unrelated rust:lint on crates/openshell-server/src/lib.rs:347 due to an existing unused shutdown_tx warning promoted to an error.

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)

[TaylorMutch]

why was this needed? There are no chart dependencies

[elezar]

why was this needed? There are no chart dependencies

When running mist helm:lint locally, this would repeatedly fail in my environment due to a stale postgresql chart. That does mean that this PR doesn't actually fix the problem (I was authoring on another host and didn't properly test it). The solution is to just remove the stale chart from deploy/helm/openshell/charts instead. I created #1957 to document this in a skill (after verifying behaviour on a host I have).