Packaging hardening: add LICENSE, remove dead vest.yaml pathing, and fix matplotlib style compatibility

[Copilot]

This PR addresses packaging/runtime breakages called out in the audit: missing LICENSE metadata target, invalid uv source override to non-existent vendor/omas, non-portable runtime fallback to dead vest.yaml, and a matplotlib style name that breaks on supported versions.

• Packaging metadata alignment

  • Added top-level LICENSE (Apache-2.0 text) to satisfy pyproject.toml license.file and README link expectations.
  • Updated setuptools package data to include vaft/.hscfg in built artifacts.

• Dependency source cleanup

  • Removed [tool.uv.sources].omas editable path override to vendor/omas (directory is not in-repo), leaving standard dependency resolution intact.

• Dead config removal and runtime behavior tightening

  • Deleted vaft/machine_mapping/vest.yaml (unused/dead, malformed).
  • Updated vaft/machine_mapping/utils.py path resolution to stop implicitly defaulting to vest.yaml; callers must provide a valid info_file, and missing files now raise explicit errors.

• Matplotlib compatibility fix

  • Replaced deprecated/removed style alias in EFIT summary workflow:

    # before
    plt.style.use('seaborn')
    
    # after
    plt.style.use('seaborn-v0_8')

• Targeted regression coverage

  • Added focused checks for:
    • LICENSE presence,
    • absence of vendor/omas override,
    • explicit info_file requirement (no hidden vest.yaml fallback),
    • updated matplotlib style string in EFIT analysis script.

[jaesun57]

@claude review pr