fix(ci): move snapshot update after build and use SYNC_PAT for sync-preview

Two fixes:
1. release-main-and-preview.yml: move `npm run test:update-snapshots`
   to after `npm run build` so tests have built artifacts available.
   Previously it ran inside the CDK sync step before the build, causing
   18 test failures.

2. sync-preview.yml: use SYNC_PAT to bypass branch protection on
   preview branch. Direct pushes were failing with GH013 rule violation.

Author: aidandaly24

.github/workflows/release-main-and-preview.yml

@@ -120,7 +120,6 @@ jobs:
                 fs.writeFileSync('$TEMPLATE_PKG', JSON.stringify(pkg, null, 2) + '\n');
               "
               echo "✅ Updated @aws/agentcore-cdk: $CURRENT_CDK -> $LATEST_CDK"
-              npm run test:update-snapshots
             fi
           fi
 
@@ -147,6 +146,9 @@ jobs:
           node scripts/generate-schema.mjs
           npx prettier --write schemas/
 
+      - name: Update snapshots
+        run: npm run test:update-snapshots
+
       - name: Create release branch and PR
         env:
           GH_TOKEN: ${{ github.token }}
@@ -219,7 +221,6 @@ jobs:
                 fs.writeFileSync('$TEMPLATE_PKG', JSON.stringify(pkg, null, 2) + '\n');
               "
               echo "✅ Updated @aws/agentcore-cdk: $CURRENT_CDK -> $LATEST_CDK"
-              npm run test:update-snapshots
             fi
           fi
 
@@ -245,6 +246,9 @@ jobs:
           node scripts/generate-schema.mjs
           npx prettier --write schemas/
 
+      - name: Update snapshots
+        run: npm run test:update-snapshots
+
       - name: Create release branch and PR
         env:
           GH_TOKEN: ${{ github.token }}

.github/workflows/sync-preview.yml

@@ -22,6 +22,7 @@ jobs:
         with:
           ref: preview
           fetch-depth: 0
+          token: ${{ secrets.SYNC_PAT }}
 
       - name: Configure git
         run: |
@@ -70,7 +71,7 @@ jobs:
       - name: Create PR for conflict resolution
         if: steps.merge.outputs.status == 'conflict'
         env:
-          GH_TOKEN: ${{ github.token }}
+          GH_TOKEN: ${{ secrets.SYNC_PAT }}
           AUTHOR_NAME: ${{ steps.author.outputs.name }}
           AUTHOR_GH: ${{ steps.author.outputs.gh_user }}
         run: |