VALUE-08A: add an artifact-owned launcher

[daniele21]

Parent: #146

Outcome

Make the existing validated ZIP materially easier to run without choosing a speculative native desktop framework.

This isolated VALUE-08A lane adds a standalone launch.py to the packaged artifact. With only Python 3.12+ available, the launcher:

• creates/reuses an artifact-owned isolated .runtime venv;
• installs runtime-requirements.txt exported from the repository lock plus the packaged wheel;
• binds runtime reuse to artifact/source/wheel/requirements identity;
• refuses to replace an unowned runtime directory;
• removes its own partial runtime after failed setup;
• execs the existing performance_lab.ui_server against the packaged built frontend;
• leaves model serving/lifecycle external.

The package RUN.md path becomes python launch.py --config <config.json>: no repository checkout, uv, Node/pnpm or manual wheel install is part of normal launch. First launch still needs package-index access and a StarterRunConfig; eliminating pre-authored JSON is VALUE-08B.

Files

• src/performance_lab/artifact_launcher.py: stdlib-only standalone launcher copied into the artifact;
• scripts/package_release.py: exports locked UI runtime requirements, ships launcher, updates artifact-owned run instructions;
• tests/test_artifact_launcher.py: artifact identity, runtime reuse/invalidation, ownership safety.

Dependency / publication gate

This is isolated preparation from dev@0b9c376f2dbcbb167f8df8488374c1b0c5d0ace2. Keep draft and do not integrate until VALUE-02D #132 PASS / VALUE-02 DONE.

Evidence boundary

Iteration CI proves launcher/package software semantics only. VALUE-08 distributed-artifact and representative install/use acceptance remain VALUE-08C/D.