determine-stacks: Brace expansion not supported in stack patterns

[stekern]

Description

The determine-stacks action does not support bash-style brace expansion in stack patterns. When users enter patterns like:

stacks/prod/{cicd-common,web-zebra,web-zebra-data}

The action fails to match any stacks because Python's Path.glob() only supports * and ** wildcards, not brace expansion.

Current behavior

Brace expansion patterns are passed directly to Path.glob() which doesn't understand them, resulting in no matches.

Expected behavior

Either:

1. Add support for brace expansion (perhaps using glob stdlib or manual expansion to avoid dependencies)
2. Update action description/README to clarify that brace expansion is not supported and show correct comma-separated syntax

Workaround

Use comma-separated paths instead:

stacks/prod/cicd-common,stacks/prod/web-zebra,stacks/prod/web-zebra-data

[falense]

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