Document local uvx packaging workflow

[dbroeglin]

Using the harness from a standalone experiment repo should not require working inside this repository or installing an editable environment first. This documents the verified uvx --from <local-checkout> workflow and fixes the wheel packaging issue that prevented local uvx installs from building cleanly.

Summary

• Remove the duplicate Hatch force-include entry so the template tree is not added to the wheel twice.
• Add local uvx --from usage to the main README and authoring guide, including PowerShell syntax.
• Carry the same guidance into newly scaffolded experiment repos through the README, AGENTS, and pyproject templates.
• Document --no-cache as the reliable way to force uv to rebuild from the local working tree while iterating.

Validation

• uv build --out-dir <artifact-dir>
• uv run pytest tests\test_scaffold.py -q
• uvx --no-cache --from <repo> copilot-experiments init <tmp-dir> --force