ci: adopt the canonical org lint gate

[Bryan Fawcett (bryanfawcett)]

What

Adopts the canonical org lint gate. .github/workflows/lint.yml is a
caller for nyuchi/.github/.github/workflows/reusable-lint.yml@main,
dropped in verbatim and not customised.

It publishes exactly the five contexts the mukoko-dev org ruleset
(id 22932468) already requires on every repo:

• lint / actionlint
• lint / JSON validity
• lint / prettier
• lint / markdownlint
• lint / yamllint

mukoko emitted none of them, so the ruleset had every PR in this
repo blocked. This PR is what unblocks it.

Config files

Landed verbatim from nyuchi/.github so every repo in the five orgs
lints identically:

• .prettierrc
• .prettierignore
• .markdownlint.jsonc
• .yamllint.yaml
• .editorconfig

Two pre-existing files were replaced by their canonical versions:

• .prettierrc — the old file set printWidth: 100 plus
  semi/singleQuote/bracketSpacing/arrowParens. The canonical file
  uses printWidth: 80 and leaves the rest at Prettier defaults. The CI
  gate only checks **/*.{md,mdx,json,jsonc}, so no TypeScript source is
  reformatted here — but note that pnpm format and the lint-staged
prettier --check hook now wrap TS/TSX at 80 rather than 100. Nothing
  in CI (pnpm turbo run build typecheck lint test) enforces Prettier;
  eslint-config-prettier only disables formatting rules, so this
  cannot break ci / Build & Test.
• .prettierignore — the old file excluded app/, honey/, and
  build-output directories. The canonical file ignores node_modules/,
  .git/, YAML (handled by yamllint/actionlint), lockfiles, and files
  with structural meaning. Build outputs are absent from a fresh CI
  checkout, and the Flutter (app/) and Python (honey/) trees contain
  no md/json that the gate would have skipped by accident.

No "prettier" key existed in package.json, so there was nothing
shadowing .prettierrc. No tracked file is shadowed by .gitignore
(checked with git ls-files | git check-ignore --no-index --stdin),
so the CLAUDE.md trap does not apply here. ci.yml publishes only
ci / Build & Test and does not compete with the lint / * contexts,
so it is untouched.

Violations fixed (not suppressed)

Run locally with CI's exact pinned versions — actionlint 1.7.12,
prettier 3.9.4, markdownlint-cli2 0.23.2, yamllint 1.38.0.

• prettier — 8 files reformatted: six services/*/wrangler.jsonc,
  web/tsconfig.json, web/vercel.json. The .jsonc files pick up
  trailing commas (valid JSONC, which is what Wrangler parses); the
  .json files do not, and lint / JSON validity still parses every
  *.json with json.load().
• markdownlint — 12 issues in 5 files.
  • MD029 (ordered-list prefix) in docs/guides/creating-mini-app.md
    and docs/guides/creating-service.md — auto-fixed.
  • MD034 (bare URLs) in web/MIGRATED.md and
    web/studio/MIGRATED.md — auto-fixed to autolinks.
  • MD036 (emphasis used instead of a heading) ×5 in ARCHITECTURE.md —
    fixed by hand, no rule disabled. The title-block and footer
    credit lines became blockquotes (they are document metadata, not
    headings) and the table caption **Total: 15 workers deployed**
    gained its sentence-ending period.
• actionlint — clean.
• yamllint — clean.
• JSON validity — clean.

Local result: RESULT rc=0.

Not done

No ruleset, branch protection, or deployment was touched.