fix(workspace): keep generated versions/* out of the root pnpm workspace

[pyramation]

Summary

pnpm-lock.yaml ping-pongs forever, and pnpm install --frozen-lockfile fails locally:

ERR_PNPM_OUTDATED_LOCKFILE  Cannot install with "frozen-lockfile" because pnpm-lock.yaml
is not up to date with <ROOT>/packages/deparser/versions/13/package.json

packages/{parser,deparser}/versions/* are generated by prepare-versions and gitignored
(packages/parser/.gitignore, packages/deparser/.gitignore) — but the root workspace globbed them:

packages:
  - 'packages/*'
  - 'packages/deparser/versions/*'   # generated + gitignored
  - 'packages/parser/versions/*'     # generated + gitignored

So workspace membership depended on whether a given machine had happened to run the generator.
A machine that had adds those importers on every install; CI's clean checkout never has the dirs
and prunes them straight back out. The diff comes back no matter which side you commit, and
git reset --hard doesn't help — gitignored dirs survive it, so the stale membership persists.

Fix is to make membership deterministic rather than incidental: drop the two globs, and have both
generators emit a pnpm-workspace.yaml into versions/ so the generated tree is a self-contained
workspace with its own (gitignored) lockfile.

 // packages/parser/scripts/prepare-versions.ts
 // packages/deparser/scripts/generate-version-packages.ts
+fs.writeFileSync(path.join(versionsDir, 'pnpm-workspace.yaml'), "packages:\n  - '*'\n");

Release flow gains one step, documented in PUBLISH.md:

npm run prepare-versions
(cd versions && pnpm install)   # once per generation, covers every version dir

The lockfile shrinks by ~2900 lines net: the last release commit had committed the versions/*
importers, which dragged in every old libpg-query / pgsql-deparser / @pgsql/types referenced
by PG 13–18 sub-packages. Removing the importers removes them too. That diff is the point of the
PR, not collateral.

Verification

• pnpm install --frozen-lockfile at the root — passes with the generated dirs present on disk,
  which is the case that used to fail
• pnpm install with the dirs present — leaves pnpm-lock.yaml untouched (the churn is gone)
• pnpm build — all 15 packages pass
• cd packages/parser/versions && pnpm install && cd 13 && npm run build — the generated tree
  still builds standalone, producing dist/{index.js,index.d.ts,esm/}

Note for anyone with an existing checkout

Generated dirs from before this change have no nested pnpm-workspace.yaml. Re-run
npm run prepare-versions (or just delete packages/{parser,deparser}/versions) to pick it up.

Link to Devin session: https://app.devin.ai/sessions/2aa454e560904773a0a6955712e0aeda
Requested by: @pyramation

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