buckets: enable Object Lock file lock when creating buckets

[goanpeca]

Summary

Expose the SDK's fileLockEnabled create-bucket option so workflows can create Object Lock-capable buckets.

Why

B2 Object Lock must be enabled when a bucket is created; it cannot be enabled later on a normal bucket. The action has retention verbs and issues for default retention, but without fileLockEnabled during bucket creation, infrastructure workflows cannot bootstrap compliant buckets end to end.

SDK support (already available)

• B2Client.createBucket({ fileLockEnabled })
• CreateBucketRequest.fileLockEnabled
• BucketInfo.fileLockConfiguration

Proposed surface

Extend the future create-bucket action from #100 with:

• file-lock-enabled (true / false, default false)

The output/summary should include the returned fileLockConfiguration so users can verify the bucket was created with Object Lock enabled.

Acceptance criteria

• create-bucket accepts file-lock-enabled.
• When true, the action passes fileLockEnabled: true to the SDK create call.
• The created bucket summary reports Object Lock status from fileLockConfiguration.
• Documentation warns that Object Lock cannot be enabled retroactively on existing buckets.
• Tests cover creating with and without file lock enabled.

Out of scope

• Setting bucket default retention, tracked in bucket defaults: default encryption and default retention #105.
• Per-object retention/legal hold, tracked in upload: support per-file Object Lock retention and legal-hold at upload time #107 and the copy Object Lock issue.