fix: mark Supabase Vault as a non-CLI provider

[artiphishle]

Summary

• change package.json#ankh.provider from the invalid free-form provider name to null
• keep @ankhorage/supabase-vault classified as a runtime secret-store adapter rather than a CLI command provider
• add a patch changeset

Root cause

The package declared ankh.provider as "supabase-vault". Current Ankh package metadata only accepts null for non-provider packages or a package-relative ./... module path for actual CLI providers.

Because the invalid non-empty string also made Doctor classify the package as CLI-capable, it emitted two cascading diagnostics for a missing src/cli/index.ts and missing ./cli export.

Validation

The resulting metadata now follows the non-provider path used by Ankh discovery:

• ankh.provider is valid (null)
• the package is no longer classified as CLI-capable
• no artificial CLI entry point or export is introduced
• branch diff is limited to package.json and one patch changeset