Drop Gatsby plugin and update pnpm workflows

[dayhaysoos]

Summary

• Remove the legacy Gatsby plugin package from the repo.
• Update pnpm workflows with a cross-platform docs dev script, release helper, and pnpm overrides.
• Purge remaining Gatsby references from contributor docs and old docs copy.

Testing

• pnpm test

[cursor]

PR Summary

Removes deprecated Gatsby plugin and streamlines tooling.

• Deletes entire gatsby-plugin-use-shopping-cart package (all source, config, and metadata)
• Updates root scripts: cross-platform dev:docs using concurrently, adds release:alpha, adjusts test/build chaining
• Moves dependency constraints to pnpm.overrides and adds packageManager field; introduces concurrently dev dependency
• Refreshes pnpm-lock.yaml (React/React DOM to 19.2.3 and related dependency alignments)
• Cleans docs: replaces Gatsby references (old docs copy tweak) and updates .env key to STRIPE_PUBLISHABLE_KEY in contributor guide

^{Written by Cursor Bugbot for commit b006f3c. This will update automatically on new commits. Configure here.}

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{Bugbot Autofix is ON. A Cloud Agent has been kicked off to fix the reported issue.}

[cursor]

Bugbot Autofix resolved the bug found in the latest run.

• ✅ Fixed: Concurrent dev:docs causes race condition on first run
  • Added initial build step before concurrent execution to ensure dist files exist before docs server starts resolving imports.

[dayhaysoos]

@cursor review

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{Bugbot Autofix is ON. A Cloud Agent has been kicked off to fix the reported issue.}

[cursor]

Bugbot Autofix resolved the bug found in the latest run.

• ✅ Fixed: Release script bumps version before running tests
  • Reordered the release:alpha script to run tests before version bump, preventing inconsistent state when tests fail.

[dayhaysoos]

@cursor review

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{Bugbot Autofix is ON. A Cloud Agent has been kicked off to fix the reported issue.}

[cursor]

Bugbot Autofix resolved the bug found in the latest run.

• ✅ Fixed: Missing lockfile update for concurrently dependency
  • Updated pnpm-lock.yaml by running pnpm install to include the missing concurrently dependency entry.

[dayhaysoos]

@cursor review