docs_generate_onboarding leaks multi-line docstrings into project structure tree

[wtthornton]

Summary

The onboarding generator's project structure tree includes full multi-line docstrings instead of truncating to the first line. This breaks the visual tree layout.

Example

Generated output included:

├── logging.py          — Structured logging setup for the server agent.
    IMPORTANT: Never log to stdout — STDIO transport uses it

The second line is a continuation of the docstring that leaked into the tree.

Expected behavior

Truncate module docstrings to the first sentence/line only in the structure tree view.

Additional issue

Same generator suggests pip install instead of uv sync even when uv.lock and .python-version exist in the project root.