[nycomp]

Summary

Convert campus from a pkgutil-style namespace package into a native PEP 420 namespace portion: delete campus/__init__.py, which contained only the pkgutil.extend_path shim and a docstring (no code, no __version__, no attribute consumers — verified by repo-wide grep). Every distribution that contributes subpackages under campus/ now ships an init-less portion, and Python merges them across sys.path.

This is the namespace groundwork for the #970 phase-3 carve (campus-common and friends as separate distributions): consumer import syntax (from campus.model import ..., import campus.common, from campus import flask_campus) is unchanged — those are submodule imports, which resolve identically under PEP 420.

Changes

• Delete campus/__init__.py — the only pkgutil reference in the codebase; its stated purpose ("extend with campus-python") is stale since the SDK installs a separate top-level campus_python namespace.
• Add scripts/audit_wheel_namespace.py — post-poetry build audit that fails the build if any wheel ships campus/__init__.py, ships .py files in a subpackage dir without __init__.py, or ships nothing under campus/. The failure mode this guards against (one stale regular package silently shadowing all other dists' portions) is otherwise invisible until runtime.
• Fix pre-existing gap caught by the audit on its first run: campus/yapper/backends/ shipped .py files with no __init__.py (accidental nested namespace portion; imported only via relative imports inside yapper). Now a regular package.
• docs/PACKAGING.md — new "Namespace Package Rules (PEP 420)" section: the init-less rule, the audit command, and the stale-venv hazard (rebuild, don't layer installs).

Testing

• 872 unit tests pass in the worktree venv
• Full contract suite passes in the worktree venv
• poetry build + python scripts/audit_wheel_namespace.py → wheel ships an init-less campus/ portion with all subpackages intact
• ruff check green on all changed/new files

Refs #970 (phase-3 groundwork; non-closing).