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

[mmcky]

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 (build-jupyter-cache: container-mode failures are silent, undebuggable, and use unpinned sub-actions #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.