chore(deps): bump actions/upload-artifact from 4 to 6 and migrate to pnpm

[Copilot]

This PR upgrades actions/upload-artifact from v4 to v6 (Dependabot update) and migrates the CI workflow from npm to pnpm to support the repository's workspace structure.

The repository uses pnpm workspaces with workspace:* protocol in package dependencies, which npm doesn't support, causing install failures.

Changes:

• Artifact action upgrade: Bump actions/upload-artifact from v4 to v6
• CI workflow: Enable Corepack, switch from npm ci to pnpm install --frozen-lockfile, update cache to pnpm
• Workspace config: Add pnpm-workspace.yaml (pnpm doesn't read package.json workspaces field)
• Package manager: Add packageManager: "pnpm@10.28.2" to package.json
• Lockfile: Generate pnpm-lock.yaml for reproducible installs

Error before:

npm ci
npm error Unsupported URL Type "workspace:": workspace:*

Fixed workflow:

- name: Enable Corepack
  run: corepack enable

- name: Setup Node.js
  uses: actions/setup-node@v6
  with:
    cache: 'pnpm'

- name: Install dependencies
  run: pnpm install --frozen-lockfile

- name: Upload contract index
  uses: actions/upload-artifact@v6

---

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[kayodebristol]

@copilot There are many duplicate draft PRs (#148-#154) all trying variants of the same CI fix and targeting the dependabot branch. Please consolidate to one clean PR targeting main, and close/supersede the rest to reduce noise. (No merges while draft.)

[Copilot]

@copilot There are many duplicate draft PRs (#148-#154) all trying variants of the same CI fix and targeting the dependabot branch. Please consolidate to one clean PR targeting main, and clo...

I understand you want to consolidate to one PR targeting main. However, I cannot:

• Create new PRs
• Close existing PRs (Fix Node 18.x CI failure: upgrade npm for workspace protocol support #148-chore(deps): bump actions/upload-artifact from 4 to 6 and migrate to pnpm #154)
• Change the base branch of an existing PR

I can only push commits to branches. The current branch (copilot/sub-pr-147-b57a5f5f-fc2b-47fb-a724-e18ff8a6e396) backs PR #154 which targets the dependabot branch.

Would you like me to:

1. Create a new branch targeting main with the fix, or
2. Have you manually change PR chore(deps): bump actions/upload-artifact from 4 to 6 #147's base from the dependabot branch to main and I can push fixes there?

The fix itself is ready - it migrates the CI from npm to pnpm with all necessary configuration files.

@copilot There are many duplicate draft PRs (#148-#154) all trying variants of the same CI fix and targeting the dependabot branch. Please consolidate to one clean PR targeting main, and clo...

I've created a clean branch fix-ci-pnpm-migration (commit 7683245) from main that consolidates the fix. This single commit:

1. Upgrades actions/upload-artifact from v4 to v6 (the Dependabot change)
2. Migrates CI from npm to pnpm (fixes workspace:* protocol issue)
3. Adds all necessary pnpm configuration files

The branch is ready locally but I cannot push it or create PRs myself.

Next steps:

1. Push this branch to create one clean PR targeting main, OR
2. Cherry-pick commit 7683245 onto the dependabot branch

Once that PR exists, PRs #148-#154 can be closed as they'll be superseded.

[kayodebristol]

Closing as superseded by #155 (single consolidated fix for the Node 18/20 CI + workspace:* issue). If we need to resurrect any approach from this PR, we can reopen.