Project association fixes

[nueces]

Summary

• Add sbx-owned VM/project metadata and guard existing VM reuse against project mismatches
• Add canonical sbx list/sbx remove with ls/rm aliases
• Add sbx doctor --fix for safe local bookkeeping repair and remove --force-start
• Extract state, doctor, VM lifecycle, runtime, and guest setup helpers out of cli.py
• Preserve main’s SmolVM notice suppression and guest clock/timezone sync behavior after rebase

Validation

• ruff check src tests
• pytest --no-cov (188 passed)