Optimize CLI startup imports for issue #108

[harumiWeb]

Summary

• lazily resolve public exports from �xstruct and �xstruct.edit to avoid front-loading heavy extraction/edit imports
• defer edit and extraction CLI implementation imports until command routing is known while keeping existing monkeypatch surfaces
• add startup isolation tests and document the lightweight CLI/package import rule

Testing

• uv run pytest tests/cli/test_cli.py tests/cli/test_edit_cli.py tests/cli/test_cli_lazy_imports.py tests/edit/test_architecture.py -q
• uv run task precommit-run

Closes #108

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[harumiWeb]

@coderabbitai review

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 5 additional findings.