docs(ci): the cross-arch _examples/ build runs locally and on GitHub

[bketelsen]

Summary

The Examples Cross-Arch Build job (examples-build, .github/workflows/ci.yml)
has cross-compiled every _examples/ program for linux/amd64 and
linux/arm64 since #70, using the same scripts/example-dirs.sh enumeration
make ci uses. Three operator-facing statements still told the reader that
build ran only in make ci:

• Makefile — the # ci comment and the ## ci help line, i.e. what
  make help prints: "the cross-arch example build runs only here";
• AGENTS.md — the "make ci only — the cross-architecture build of every
  _examples/ program…" bullet, which already contradicted AGENTS.md's own
  CI-jobs paragraph and docs/design/quality-loop.md;
• docs/org-adrs.md — the ADR-0038 entry: "while the cross-arch example build
  runs only locally".

Makefile's own comment requires those three to say the same thing; #70 updated
ci.yml, AGENTS.md's CI-jobs paragraph, and quality-loop.md, but not these.
This corrects all three, adds the job to docs/design/overview.md's two CI job
enumerations (it was missing from both), and pins the claim in
scripts/check-docs.mjs next to the existing release-config consistency check
so the local-only wording cannot come back while the job exists.

No workflow, Makefile recipe, or Go source behavior changes.

Checks

• make check — not run: this is a docs-only change and make check
  rewrites files with gofmt -w. make verify (the non-mutating gate,
  which also runs go mod tidy -diff) was run instead and is green — see
  Verification.
• go test -race -short ./... — covered by CI's Race Detection job; no Go
  source is touched by this PR.
• go.mod still declares no dependencies (stdlib only) — unchanged
• New or changed behavior has focused tests, including failure paths: the
  new scripts/check-docs.mjs check is demonstrated failing on each of the
  four doc edits reverted individually — see Verification

Docs housekeeping

• AGENTS.md, docs/design/overview.md, docs/specs/* updated for
  behavior or convention changes (AGENTS.md, docs/design/overview.md,
  docs/org-adrs.md)
• Conformance aliases (ADR-0001) untouched — canonical targets edited
  instead

Protected boundaries

N/A — no .github/workflows/**, .goreleaser.yaml, .svu.yaml, or
policies/agent-governance.json touched. ci.yml is read by the gate script,
never modified.

Verification

• node scripts/check-docs.mjs green:

  ok   docs_index_coverage: 1.000 (required 1)
  ok   link_integrity: 1.000 (required 1)
  ok   symlink_resolution: 1.000 (required 1)
  checked: 12 docs, 154 links, 9 symlinks
  

• The new gate actually pins the claim. Reverting each of the four doc
  edits in turn (git checkout HEAD~1 -- <file>) makes the gate exit 1:

  ### revert Makefile
  FAIL cross-arch: Makefile calls the cross-arch _examples/ build local-only ("runs only here") while .github/workflows/ci.yml runs it in the examples-build job
  ### revert AGENTS.md
  FAIL cross-arch: AGENTS.md calls the cross-arch _examples/ build local-only ("`make ci` only") while .github/workflows/ci.yml runs it in the examples-build job
  ### revert docs/org-adrs.md
  FAIL cross-arch: docs/org-adrs.md calls the cross-arch _examples/ build local-only ("runs only locally") while .github/workflows/ci.yml runs it in the examples-build job
  ### revert docs/design/overview.md
  FAIL cross-arch: docs/design/overview.md does not name the Examples Cross-Arch Build job that .github/workflows/ci.yml defines
  

  (each run exited 1; the tree was restored and the gate returned to exit 0)
• make verify green:

  ==> verify: go.mod is tidy
  go mod tidy -diff
  ==> verify: gofmt
  ==> verify: golangci-lint 2.13.1 (built with go >= 1.26.7)
  0 issues.
  0 issues.
  go vet ./...
  go vet ./_examples/deploy ./_examples/fileprocess ./_examples/healthcheck ./_examples/migration
  ==> verify: tests
  go test ./...
  ok  	github.com/frostyard/std/reporter	0.002s
  ok  	github.com/frostyard/std/tests/e2e	3.033s
  

• make help's ci row now reads: "…the cross-arch example build is also
  run on GitHub by the Examples Cross-Arch Build job) (core ADR-0038)"
• Checked against the
  PR review rubric

Risk classification

Low. Documentation and one added docs-gate assertion. No Go source, no
Makefile recipe body, no workflow, no threshold, and no gate weakened — the
gate only gains a check.