docs(ci-cd-pipeline): point at a living workflow instead of a fossil snippet

[os-warren]

Fixes #6308

content/docs/guide/ci-cd-pipeline.md's "Adding a New Workflow" section told a
contributor to "follow the existing pattern for pnpm + Turbo setup" and then gave a copied
YAML block in which every line had drifted from what any workflow in this repository
actually does.

Re-measured on this PR's own HEAD (6d551e44e merge-base, after merging #6402)

$ grep -rn "actions/setup-node@" .github/workflows/ | sed -E 's/.*(actions\/setup-node@[^ ]+).*/\1/' | sort | uniq -c
     28 actions/setup-node@v7

$ grep -rn "node-version:" .github/workflows/ | sed -E "s/.*node-version:\s*//" | sort | uniq -c
      1 '22'
     27 '22.x'

$ grep -rn "pnpm/action-setup" .github/workflows/ | wc -l
0

$ grep -n '"engines"' -A3 package.json
  "engines": {
    "node": ">=22.11",
    "pnpm": ">=10"
  },

snippet said	measured reality (fresh, not the card's 090927f4f figures)
actions/setup-node@v4	@v7 — 28 occurrences, no other version (up from the card's 27 — #6402 added docs-route-eager-closure.yml today, one more setup-node@v7)
node-version: 20	'22.x' × 27, '22' × 1 — and 20 is below the engines.node floor of >=22.11
pnpm/action-setup@v4	0 occurrences anywhere. pnpm comes from corepack enable (14 workflows) + root packageManager: pnpm@10.31.0

What changed

A copied YAML block is a fossil the moment it's pasted, so the section no longer repeats
one. It now points at readme-exports.yml as the living example — chosen because it
is small, PR-triggered (not scheduled, unlike e.g. spec-range-floors.yml), and its setup
is the complete pattern most new build/test/lint workflows need: checkout, corepack enable, actions/setup-node with pnpm's own cache, pnpm install --frozen-lockfile, then
a turbo run build step. (The repo's other cheap-tier gates — control-bytes.yml,
changeset-presence.yml — deliberately skip install/build, so they don't demonstrate the
"pnpm + Turbo" pattern this section is teaching.)

Only the two steps that hold regardless of which Node/pnpm version the repo is on when
read stay quoted on the page — checkout and corepack enable — everything
version-specific (Node version, cache key, install command) is now "read it from the
workflow" rather than copied here.

No new version literal was introduced — the replacement names a workflow file, not a
Node/pnpm version, so no doc-version-claims.test.ts KNOWN_CLAIMS entry was needed. (The
existing ci-cd-pipeline.md / 'Node 22.x' anchored entry at line ~199, "Uses: Node
22.x, pnpm via corepack", is untouched by this PR.)

Correcting the record on "why nothing caught this": the issue and dispatch both said
doc-version-claims.test.ts "skips fences by design." On this HEAD that's no longer
accurate — the file's own header says "Fences are SCANNED... the opposite of
check-doc-links.mjs, on purpose" and the scan loop does call collect() on fenced lines.
The real reason nothing caught this snippet: none of its three false lines match the
ledger's TOOLCHAIN + SEP + VERSION regex regardless of fencing —
actions/setup-node@v4 has @ between the toolchain word and the version (not in SEP's
character class), pnpm/action-setup@v4 has /action-setup@ in the way, and
node-version: 20 has the literal word version between node and 20, which SEP
also can't cross. Re-verified by running the two-file targeted suite before and after the
edit (both green — see Tests).

Tests

Full tree (per dispatch instruction — this page carries ci-cd-pipeline-doc.test.ts,
merge-queue-reporting.test.ts (#4154), and the version-literal ledger, and a subset
chosen from just this snippet's subject matter would miss the ones that fire on the page
as a whole, per today's #6402 rework):

$ pnpm exec vitest run scripts/__tests__
 Test Files  80 passed (80)
      Tests  2303 passed (2303)

(HEAD 54fc0c337, git rev-parse --short HEAD.)

Plus targeted doc gates over the edited page:

$ pnpm check:doc-fences   → ✅ (223 docs scanned)
$ node scripts/check-doc-links.mjs → Links are valid across 17 scan roots.
$ pnpm check:doc-types    → ✅ Every documented component type is registered.
$ node scripts/check-changeset-presence.mjs → ✅ 1 changeset added
$ grep -naP '[\x00-\x08\x0b\x0c\x0e-\x1f\x7f]' content/docs/guide/ci-cd-pipeline.md .changeset/6308-living-workflow-example.md
  (no output — clean)

Notes

• Branched from main after confirming Weigh the docs-site eager closure structurally (#6316) #6402 (docs-route-eager-closure.yml) had landed,
  per this card's dispatch order — fast-forward merge, no rebase, no force-push.
• #6280 (stale check-doc-links coverage claims on the same page) is explicitly out of
  scope per the dispatch order's fold decline; not touched here.
• Draft — this seat arms it per the dispatch order.

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