refactor: split cli.py into command layer + catalog/config/validator services #30

Surfaced by the design/security review on #25.

cli.py is ~3k lines; catalog, config, and validator logic are entangled and only testable through the CLI. The shared validator (used by both catalog validate and CI) is the clearest candidate for extraction.

Proposal

• catalog.py — load/search/install/mapping
• config.py — load/save, --profile/env/active precedence
• validator.py — the shared validator
• cli.py — command registration only

Acceptance

• Modules extracted; behavior unchanged
• Validator importable/testable in isolation
• Full suite still green

Effort: M