fix: render KMS backend label in closed select

[reatang]

Pull Request

Description

The KMS backend dropdown (id="kmsBackend") on the SSE settings page rendered the raw option value (e.g. vault-transit) instead of the translated SelectItem label ("HashiCorp Vault Transit Engine") until the dropdown was opened for the first time.

Root cause: components/ui/select.tsx passes SelectPrimitive.Value straight through, and base-ui's Select.Value renders the value itself when it has no children/items mapping — the label only becomes available to it after the popup mounts.

Fix: add a backendTypeLabels map (typed Record<ConfigFormState["backendType"], string>) and pass the current label as SelectValue children, following the established pattern in app/(dashboard)/_components/performance-server-list.tsx (sortLabels). The SelectItem labels now reference the same map so the strings are defined once.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Code refactoring
• Performance improvement
• Test improvements
• Security fix

Testing

• Unit tests added/updated
• Manual testing completed

pnpm test:run

Quality gates all run via corepack pnpm@11.11.0: type-check ✅, lint ✅, test:run ✅ (401 passing). format:check only reports the pre-existing components/object/tiff-viewer.tsx issue already present on main; the changed file passes Prettier.

Verified visually in next dev against a local rustfs instance: on first render (dropdown never opened) the trigger now shows the translated label instead of vault-transit; opening the dropdown shows all four labeled options; selecting another backend updates the trigger label immediately.

Checklist

• Code follows the project's style guidelines
• Self-review completed
• TypeScript types are properly defined
• All commit messages are in English (Conventional Commits)
• All existing tests pass
• No new dependencies added, or they are justified

Related Issues

N/A

Screenshots (if applicable)

N/A

Additional Notes

Other SelectValue usages that pass no children (e.g. components/buckets/info.tsx, components/lifecycle/new-form.tsx) have the same latent behavior; this PR intentionally only fixes the reported SSE instance.