chore: add skills sync workflow

Author: felipefreitag

.github/workflows/sync-skills.yml

@@ -0,0 +1,88 @@
+name: Sync Skills
+
+on:
+  push:
+    branches: [main]
+    paths: ['skills/**']
+  workflow_dispatch:
+
+concurrency:
+  group: sync-skills
+  cancel-in-progress: false
+
+jobs:
+  sync:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout source repo
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd
+        with:
+          path: source
+
+      - name: Checkout resend-skills
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd
+        with:
+          repository: resend/resend-skills
+          token: ${{ secrets.SYNC_SKILLS_TOKEN }}
+          path: target
+
+      - name: Compare skills
+        id: diff
+        run: |
+          changed=false
+          for skill_dir in source/skills/*/; do
+            skill_name=$(basename "$skill_dir")
+            target_dir="target/skills/$skill_name"
+
+            if [ ! -d "$target_dir" ]; then
+              echo "New skill: $skill_name"
+              changed=true
+              continue
+            fi
+
+            # Compare only spec-compliant files: SKILL.md, references/, scripts/, assets/
+            for item in SKILL.md references scripts assets; do
+              src="$skill_dir/$item"
+              dst="$target_dir/$item"
+              if [ -e "$src" ] && ! diff -rq "$src" "$dst" > /dev/null 2>&1; then
+                echo "Changed: $skill_name/$item"
+                changed=true
+              fi
+            done
+          done
+
+          echo "changed=$changed" >> "$GITHUB_OUTPUT"
+
+      - name: Copy skills and open PR
+        if: steps.diff.outputs.changed == 'true'
+        env:
+          GH_TOKEN: ${{ secrets.SYNC_SKILLS_TOKEN }}
+        run: |
+          cd target
+
+          git config user.name "github-actions[bot]"
+          git config user.email "github-actions[bot]@users.noreply.github.com"
+          git checkout -b sync/resend-cli-${{ github.sha }}
+
+          for skill_dir in ../source/skills/*/; do
+            skill_name=$(basename "$skill_dir")
+            rm -rf "skills/$skill_name"
+            mkdir -p "skills/$skill_name"
+
+            # Copy only spec-compliant files
+            cp "$skill_dir/SKILL.md" "skills/$skill_name/"
+            for dir in references scripts assets; do
+              if [ -d "$skill_dir/$dir" ]; then
+                cp -r "$skill_dir/$dir" "skills/$skill_name/"
+              fi
+            done
+          done
+
+          git add skills/
+          git commit -m "sync: resend-cli skills from ${GITHUB_SHA::7}"
+          git push origin sync/resend-cli-${{ github.sha }}
+
+          gh pr create \
+            --repo resend/resend-skills \
+            --title "Sync resend-cli skills" \
+            --body "Automated sync from [resend/resend-cli@\`${GITHUB_SHA::7}\`](https://github.com/resend/resend-cli/commit/${{ github.sha }})."