Backblaze test() always fails: probe path references unresolved {bucket}

[AtelyPham]

Summary

backblazeConnector.test() can never succeed: the health-check probe path references {bucket}, which is not available at connect time, so interpolate throws and test() returns { ok: false, reason: "missing required argument: bucket" }. A Backblaze connection therefore never validates as healthy.

Pre-existing (the probe path predates #118; under the old Bearer auth it would have thrown the same way), surfaced during the SigV4 work (#113 / #118).

Evidence

• src/connectors/adapters/backblaze.ts — test: { method: 'GET', path: '/{bucket}?list-type=2&max-keys=1' }.
• adapter.test() calls executeRestRequest with args: {} (declarative-rest.ts), and the credential bundle parsed by parseAwsCredentialBundle carries only accessKeyId/secretAccessKey/region/sessionToken/endpoint — no bucket. metadata is not merged into args, so {bucket} is unresolvable.

Repro

backblazeConnector.test({ credentials: { kind:'api-key', apiKey: JSON.stringify({ accessKeyId, secretAccessKey, region:'us-west-001' }) }, ... })
// → { ok: false, reason: "missing required argument: bucket" }

Suggested fix

Use a bucket-independent probe (e.g. GET / ListBuckets if Backblaze's S3-compatible API supports it), or source the configured bucket from connection metadata / the credential bundle and inject it into the test args so {bucket} resolves.

Refs #113, #118.