Align dispatch release and preview workflows

[PatrickJS]

Summary

• Add PR preview, main snapshot, stable GitHub Packages/npm publish, release doctor, and GitHub Pages jobs to the pipeline-owned workflow.
• Sync package scripts from pipeline.js and commit the pipeline task lock.
• Keep pnpm-first README examples and route development checks through generated pnpm run pipeline:* scripts.
• Add a small README-backed Pages build task until @async/pipeline owns README-to-Pages generation.

Verification

• pnpm install --frozen-lockfile
• pnpm async-pipeline sync generate
• pnpm run pipeline:sync:check
• pnpm run pipeline:github:check
• pnpm run pipeline:task:docs.site
• pnpm run pipeline:verify
• git diff --cached --check

Repo Settings

• Enabled GitHub Pages for async/dispatch with build_type=workflow (https://async.github.io/dispatch/).

[github-actions]

Preview package

Preview for PR head 112744516ab1af1cd9c954f7c719a8876733b04e (built from its merge with main), published to GitHub Packages as @async/dispatch.

Latest successful build for this PR:

pnpm add @async/dispatch@pr-1

Exact commit build:

pnpm add @async/dispatch@0.0.0-pr.1.sha.112744516ab1af1cd9c954f7c719a8876733b04e

Requires GitHub Packages auth and @async:registry=https://npm.pkg.github.com in your npm config.