docs: point at markfluence-action and delete the CI document

[willkg]

markfluence-action shipped as v1.0.0, and mozilla/markfluence-demo publishes through it. So markfluence stops documenting how to hand-roll a CI workflow and points at the thing that does it.

mozilla/markfluence-action#8 landed first and moved this page's unique content into the action's README, so there is no window where neither repository documents it.

docs/github-actions.md is deleted

It predated the action — it taught the hand-rolled recipe and accumulated the reasoning for why a CI publish is shaped the way it is. Keeping it now means maintaining a parallel implementation of what the action does.

That copy had already rotted, which is the argument rather than an aside. It carried three bugs the action had fixed and it had not:

• a "publish everything" fallback that diffed against the first commit, and so omitted any file added in that commit and never touched since
• a plain docs/**/*.md pathspec, which as a git pathspec silently misses top-level files
• a newline-delimited list through bare xargs, which splits docs/release notes.md into two arguments and aborts outright on an apostrophe

Anyone who pasted that recipe got all three. I fixed them in the action months of work ago and never here, which is precisely the failure mode a second copy has.

Where its content went

Everything a consumer needs is in the action's README as of that PR: the service-account recommendation and why a personal token is the wrong one; whether the repository is even the right source of truth, and the explicit do not run this when it is not; the note-on-the-page convention; what --force overrides and why the second check makes it non-optional; the two republishing costs beyond watcher mail; exit codes and the skipped-not-failed contract; and the page_id prerequisite.

The hand-rolled recipe is not carried anywhere, deliberately. The action's README is user documentation for people using the action, and a recipe for not using it does not belong there.

That loses nothing. Three of its four gotchas — deletions, the empty-list guard, -z/xargs -0 — are the action's own internals a user never touches. The fourth, the :(glob) pathspec prefix, is user-facing and is documented under How files works. All four remain in publish/publish.sh's comments, which is where reasoning about the implementation belongs.

What markfluence keeps

A "Publishing from CI" section under Usage — a working step and a pointer — because that is where someone looking for CI will look, and a bare link from a docs table is not enough. The pages: block that makes it take no per-file inputs stays documented here, since that is markfluence's own feature.

CLAUDE.md records that there is deliberately no CI document here, and why, so the next person does not helpfully recreate one.

Reference cleanup, also in this PR

• CLAUDE.md no longer says the action has not shipped; _plans/047 no longer reads as pending.
• .goreleaser.yaml and release.yml called it "Ship markfluence as a reusable GitHub Action #29's action" — naming the repository is clearer now that it exists, and the tag-glob rationale in both now says the moving major tag lives in markfluence-action and never here.
• The coupling list — the five things here the action reads, which make check cannot verify — is unchanged, and still the point of that CLAUDE.md paragraph.

_plans/ still references the deleted file by name in three places. Left alone: those are the record of what was true when each plan was written.

After this

#29 can close with a pointer, and markfluence-demo's # FIXME can go from @main to @v1.