`vix run` defaults to `dev-ninja` instead of reusing last build preset

[GaspardKirira]

Problem

After running vix build with a specific preset, vix run could still default
to dev-ninja instead of reusing the last successful build preset.

Impact

• Inconsistent behavior between vix build and vix run
• Surprising rebuilds or wrong build-dir selection
• Confusing results in iterative workflows

Fix (v1.17.7)

• vix run now reuses the last successful build preset instead of
  defaulting to dev-ninja.

Verification

• Build with a custom preset, then run without specifying preset:
  • Expected: run uses the same preset/build-dir as last build
  • Actual (v1.17.7): ✅ consistent