refactor(cmd): split molecule.go into focused files
Split the 1929-line molecule.go into 5 focused files:
- molecule.go (376): command definitions, init(), loadMoleculeCatalog
- molecule_status.go (673): status, progress, current commands
- molecule_list.go (432): list, show, export, parse, instances
- molecule_lifecycle.go (359): instantiate, catalog, burn, squash
- molecule_attach.go (128): attach, detach, attachment
No functional changes - pure refactoring for maintainability.
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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