Track bundle sizes across builds

Record bundle sizes across all packages and track through time so that

1. any upward drift of bundle sizes over time can be nipped in the bud
2. we catch accidental 'bundle bloat', caused by unintentional imports from non-peer packages, which cause source packages to be bundled.

No files, tests, or entry points are named. Start by locating how all packages are built and where builds run in automation, then determine how bundle sizes can be recorded over time. Done means every package is tracked and upward drift or accidental inclusion of non-peer source packages is detectable.

Written by the indexing model from the issue text.