ci: regenerate skills via GitHub Actions instead of Cloud Build

Replaces the Cloud Build pipeline (which needed SSH keys and Secret Manager tokens) with a GitHub Actions workflow. On PRs that bump toolbox_version.txt, it regenerates skills and commits them back to the PR branch using the built-in GITHUB_TOKEN. Moves the generator script under .github/scripts/.

Author: twishabansal

.ci/skills-gen.cloudbuild.yaml

@@ -0,0 +1,56 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+name: Generate Skills
+
+on:
+  pull_request:
+    paths:
+      - "toolbox_version.txt"
+
+jobs:
+  generate-skills:
+    # Only run for same-repo PRs (e.g. renovate's toolbox bump), where the
+    # built-in GITHUB_TOKEN can push back to the PR branch.
+    if: github.event.pull_request.head.repo.full_name == github.repository
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+    steps:
+      - name: Check out PR branch
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
+        with:
+          ref: ${{ github.head_ref }}
+
+      - name: Generate skills
+        run: |
+          VERSION="$(tr -d '\n' < toolbox_version.txt)"
+          echo "Detected toolbox version: $VERSION"
+          export VERSION
+          chmod +x ./.github/scripts/generate_skills.sh
+          ./.github/scripts/generate_skills.sh
+
+      - name: Commit and push regenerated skills
+        run: |
+          if [ -z "$(git status --porcelain)" ]; then
+            echo "No skill changes generated. Nothing to commit."
+            exit 0
+          fi
+
+          echo "Changes detected. Committing regenerated skills..."
+          git config user.name "github-actions[bot]"
+          git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
+          git add .
+          git commit -m "chore: auto-generate skills for toolbox v$(tr -d '\n' < toolbox_version.txt)"
+          git push