Fixes resolving boards in nested directories.

[PaulKinlan]

Fixes #595

• There was a bug where the directory loader wouldn't be able to load directories properly because a base in new URL requires / which is not something that is returned from dirent
• Updates the boards to migrate away from llm-starter
• When saving files in folders underneath the current output directory, put them next to the json (or at least map the directory structure relative to the root).
• Removes the experimental YAML board format because it will get in the way of recursive loading.

[changeset-bot]

🦋 Changeset detected

Latest commit: 5db4a14

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@google-labs/breadboard-cli	Minor
@google-labs/breadboard-hello-world	Patch

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