build-lectures: `-n` (nitpick) absent from default strictness; no extra-args passthrough via build-jupyter-cache

From the v0.8.0 validation study against native lecture-python-intro / lecture-python-programming. Context: QuantEcon/lectures#11.

build-lectures defaults extra-args to -W --keep-going (build-lectures/action.yml:25) — no -n. HTML-only gap: :103-104 hard-codes -n for pdflatex and jupyter, and only the html branch (:102) leaves builder_args empty, so the published site builds without nitpick. build-jupyter-cache calls build-lectures at three fixed with: blocks with no extra-args passthrough (build-jupyter-cache/action.yml:160-190), so its consumers cannot get -n — or any flag — in.

Native practice is not uniform:

• lecture-python-programming ci.yml:87 + publish.yml:103 — -n -W --keep-going
• lecture-python-intro ci.yml:86 — -nW --keep-going; publish.yml:91 — none, neither -n nor -W
• both repos' cache.yml — -W --keep-going

So the default already equals both native cache builds and is stricter than intro's publish; -n diverges only on the CI/publish HTML path, which a direct build-lectures consumer can override.

templates/ci.yml:82 and templates/publish.yml:98 hard-code extra-args: '-W --keep-going', and extra-args replaces rather than extends the default (build-lectures/README.md:190-203): changing the default is a no-op for template-derived consumers, and adding -n but dropping -W silently loses build-failure detection.

Decisions needed before any code

• Org strictness for HTML builds — add -n? Standardization, not a parity fix, and consumer-visible: repos with broken cross-references start failing CI, so it wants an announcement and a minor release.
• Passthrough shape — a per-builder html-extra-args beats a blanket extra-args, since pdflatex and jupyter already inject -n and would get it twice.

Then, in this order

• Apply the decided strictness to templates/ci.yml:82 and templates/publish.yml:98 — that is what reaches consumers.
• Add the passthrough to build-jupyter-cache/action.yml:42-51, wired at :168/:178/:188, mirroring the upload-failure-reports plumbing from v0.11.0 (#83); update the reproduce commands at :439-443, whose comment (:438) requires them to match today's flags. templates/cache.yml:62 inherits the gap and cannot carry the strictness decision until then.
• Document the native-equivalent invocation in docs/MIGRATION-GUIDE.md, which never mentions extra-args; the only nitpick guidance is the "Nitpick mode" example at build-lectures/README.md:212.

Read build-lectures/action.yml, build-jupyter-cache/action.yml, the CI, publish, and cache templates, and the README sections on extra-args. Compare the existing builder arguments with the reproduce commands at build-jupyter-cache/action.yml:439-443, then confirm the strictness and passthrough decisions before changing anything. Done means the chosen flags reach the relevant consumers, the cache action exposes the agreed arguments, and the migration guidance and reproduction commands match.