chore: migrate from npx to pnpm

[daniel-graham-amplitude]

Summary

Update the semantic-release task to use deterministic dependencies.

Migrates from using npx with -p flag to using pnpm with package.json + lockfiles.

Checklist

• Does your PR title have the correct title format?
• Does your PR have a breaking change?: No

[Copilot]

Pull request overview

This PR migrates the semantic-release task from using npx with the -p flag to using pnpm with a package.json and lockfile for deterministic dependency management.

Key changes:

• Replaced npx calls with pnpm install + pnpm exec in the release workflow
• Added package.json to declare semantic-release dependencies explicitly
• Added pnpm-lock.yaml (v9.0) for dependency locking
• Added pnpm-workspace.yaml for workspace configuration

Reviewed changes

Copilot reviewed 3 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
.github/workflows/release.yml	Updated release workflow to use pnpm instead of npx; added pnpm setup step
package.json	New file defining semantic-release dependencies as devDependencies
pnpm-lock.yaml	New lockfile (v9.0) with frozen dependency tree for deterministic installs
pnpm-workspace.yaml	New workspace configuration file
.gitignore	Added node_modules/ to ignore installed dependencies

Files not reviewed (1)

• pnpm-lock.yaml: Language not supported

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.