feat: add --snapshot flag to npm run package

[Hweinstock]

Description

Problem

PR tarballs from different commits all have the same version (0.8.0), making it impossible to identify which commit a tarball came from once downloaded.

Solution

Add a package npm script (scripts/package.mjs) that wraps build + pack. When invoked with --snapshot, it appends the short git commit hash to the version (e.g. 0.8.0-sha.abc1234) so pre-release tarballs are self-documenting. The PR tarball workflow now uses this script.

Related Issue

N/A

Documentation PR

N/A

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Other (please describe):

Testing

How have you tested the change?

• I ran npm run test:unit and npm run test:integ

• I ran npm run typecheck

• I ran npm run lint

• If I modified src/assets/, I ran npm run test:update-snapshots and committed the updated snapshots

• npm run package produces aws-agentcore-0.8.0.tgz

• npm run package -- --snapshot produces aws-agentcore-0.8.0-sha.6e19463.tgz

• package.json version restored correctly after snapshot build

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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