Repoint mlsysim.core.<engine-mod> -> mlsysim.engine.<mod>, the
from-mlsysim.core-import-calibration form, and mlsysim.infra -> mlsysim.infrastructure
across the deferred consumers: docs prose + tutorials, tutorial slides/cheatsheet/
exercises, paper.tex, README, cli/DESIGN.md, and the mlsysim_constants audit README.
Also fix two docstrings inside the moved engine modules (calibration.py, pipeline.py)
that still named the old core paths. Update the quartodoc config (sections list) to
the new module paths and add the engine package.
NOTE: the generated quartodoc API stubs under mlsysim/docs/api/ (core.*.qmd,
infra*.qmd) still carry the old paths — they regenerate from the updated config via
`quartodoc build` (toolchain not installed in this worktree), so they are left
untouched here rather than hand-edited. Run `quartodoc build` to refresh them.
482 passed; import clean.
Delete the catch-all defaults module and relocate assumptions into
Literature, Systems, Infrastructure, Ops, Platforms, and core.calibration.
Update textbook QMD cells, labs, audit tooling, and CI gates so registry
paths are authoritative with no package-root aliases or defaults shims.
