Add Forgejo Actions workflow for automatic upstream sync

Runs weekly (Sunday 06:00 UTC) or on manual trigger.
Uses GITEA_TOKEN auto-provided by Forgejo Actions to push back.

.forgejo/workflows/sync-upstream.yml

@@ -0,0 +1,63 @@
+name: Sync Upstream Skills
+
+on:
+  schedule:
+    # Weekly: Sunday 06:00 UTC
+    - cron: '0 6 * * 0'
+  workflow_dispatch:
+
+jobs:
+  sync:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout from Forgejo
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          # Forgejo Actions auto-provides GITEA_TOKEN for the current repo
+          token: ${{ secrets.GITEA_TOKEN }}
+
+      - name: Add upstream remote
+        run: |
+          git remote add upstream https://github.com/obra/superpowers.git
+          git fetch upstream --depth=1
+
+      - name: Sync selected skills
+        id: sync
+        run: |
+          SKILLS="
+            systematic-debugging
+            test-driven-development
+            verification-before-completion
+            writing-plans
+            requesting-code-review
+            receiving-code-review
+            finishing-a-development-branch
+          "
+
+          CHANGED=false
+          for skill in $SKILLS; do
+            diff_files=$(git diff --name-only HEAD upstream/main -- "skills/$skill" 2>/dev/null || true)
+            if [ -n "$diff_files" ]; then
+              echo "Updating skills/$skill..."
+              git checkout upstream/main -- "skills/$skill"
+              git add "skills/$skill"
+              CHANGED=true
+            fi
+          done
+
+          if [ "$CHANGED" = true ]; then
+            echo "changed=true" >> $GITHUB_OUTPUT
+          else
+            echo "changed=false" >> $GITHUB_OUTPUT
+          fi
+
+      - name: Commit and push
+        if: steps.sync.outputs.changed == 'true'
+        run: |
+          git config user.name "forgejo-actions[bot]"
+          git config user.email "forgejo-actions@git.vpsj.de"
+
+          UPSTREAM_SHA=$(git rev-parse --short upstream/main)
+          git commit -m "Sync skills from obra/superpowers upstream (${UPSTREAM_SHA})"
+          git push origin main