Pin pnpm to 10.30.0 in workflows; remove packageManager from package.json

Having both packageManager in package.json and version in the action causes
ERR_PNPM_BAD_PM_VERSION. Single source of truth: version: 10.30.0 in workflows.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ctrimm

.github/workflows/co2-emissions-cron.yml

@@ -15,7 +15,7 @@ jobs:
       - name: Install pnpm
         uses: pnpm/action-setup@v4
         with:
-          version: 10
+          version: 10.30.0
 
       - name: Setup Node.js
         uses: actions/setup-node@v4

.github/workflows/deploy.yml

@@ -35,7 +35,7 @@ jobs:
       - name: Install pnpm
         uses: pnpm/action-setup@v4
         with:
-          version: 10
+          version: 10.30.0
 
       - name: Setup Node.js
         uses: actions/setup-node@v4

package.json

@@ -8,8 +8,7 @@
   },
   "type": "module",
   "version": "1.0.0",
-  "packageManager": "pnpm@10.30.0",
-  "engines": {
+"engines": {
     "node": ">=20"
   },
   "scripts": {