ci: adopt the canonical org lint gate

[Bryan Fawcett (bryanfawcett)]

This repo published none of the five lint / * contexts the nyuchi org
ruleset requires on the default branch, so nothing could merge.
.github/workflows/lint.yml is now the canonical thin caller for
nyuchi/.github/.github/workflows/reusable-lint.yml. The job is named
lint and calls a reusable, so the checks publish as
lint / <called job> — exactly the five required strings.

Config files added, byte-identical to nyuchi/.github: .prettierrc,
.prettierignore, .markdownlint.jsonc, .yamllint.yaml, .editorconfig.

actionlint, JSON validity and yamllint were already clean. markdownlint
found two MD031 blanks-around-fences issues in packages/ui/BUILDING.md,
auto-fixed, and prettier reformatted two more markdown files. No hand
fixes were needed.

This repo carries a pnpm-lock.yaml, which the canonical .yamllint.yaml
now ignores alongside package-lock.json and yarn.lock — lockfiles are
generated, and pnpm copies registry deprecation notices into them
verbatim at lengths no one can rewrap.

Verified locally with CI's exact pinned versions (actionlint 1.7.12,
prettier 3.9.4, markdownlint-cli2 0.23.2, yamllint 1.38.0): all five
clean.

Co-Authored-By: Claude Opus 5 (1M context) noreply@anthropic.com

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