ci: daily auto-sync from upstream rtk-ai/rtk

Merges upstream/master into our master once a day (06:00 UTC).
On clean merge, pushes automatically. On conflict, opens a GitHub
issue labelled upstream-sync so it can be resolved manually.

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

Author: 0xClandestine

.github/workflows/sync-upstream.yml

@@ -0,0 +1,78 @@
+name: Sync upstream
+
+on:
+  schedule:
+    - cron: '0 6 * * *'  # daily at 06:00 UTC
+  workflow_dispatch:      # allow manual trigger
+
+permissions:
+  contents: write
+
+jobs:
+  sync:
+    name: Merge upstream/master
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: master
+          fetch-depth: 0
+          token: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Configure git
+        run: |
+          git config user.name  "github-actions[bot]"
+          git config user.email "github-actions[bot]@users.noreply.github.com"
+
+      - name: Add upstream remote
+        run: git remote add upstream https://github.com/rtk-ai/rtk.git
+
+      - name: Fetch upstream
+        run: git fetch upstream master
+
+      - name: Merge upstream/master
+        id: merge
+        run: |
+          if git merge --no-edit upstream/master; then
+            echo "merged=true" >> "$GITHUB_OUTPUT"
+          else
+            echo "merged=false" >> "$GITHUB_OUTPUT"
+            git merge --abort
+          fi
+
+      - name: Push if merged cleanly
+        if: steps.merge.outputs.merged == 'true'
+        run: git push origin master
+
+      - name: Open issue on conflict
+        if: steps.merge.outputs.merged == 'false'
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const title = 'Upstream sync conflict — manual merge required';
+            const { data: issues } = await github.rest.issues.listForRepo({
+              owner: context.repo.owner,
+              repo:  context.repo.repo,
+              state: 'open',
+              labels: 'upstream-sync',
+            });
+            if (issues.some(i => i.title === title)) return; // already open
+            await github.rest.issues.create({
+              owner: context.repo.owner,
+              repo:  context.repo.repo,
+              title,
+              labels: ['upstream-sync'],
+              body: [
+                '`sync-upstream` workflow failed to auto-merge.',
+                '',
+                'Run locally to resolve:',
+                '```',
+                'git fetch upstream',
+                'git merge upstream/master',
+                '# fix conflicts',
+                'git push',
+                '```',
+                '',
+                `Triggered by run: ${context.serverUrl}/${context.repo.owner}/${context.repo.repo}/actions/runs/${context.runId}`,
+              ].join('\n'),
+            });