fix: support create command from bare repositories

[corwinm]

Summary

• detect bare vs non-bare invocation context for arashi create and resolve execution/config loading paths accordingly
• add repository-content config fallback for bare repositories and actionable guidance for missing setup/conflicts
• add unit and integration regression coverage for bare-root success, fallback resolution, conflict handling, and rollback guarantees
• handle CI environments where bare HEAD points to an unset branch by validating branch existence before tracked-file reads

Validation

• bun run lint
• bun test
• bun run build

Closes corwinm/arashi-arashi#57

[github-actions]

🎉 This PR is included in version 1.4.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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