ci(ci): add Close Topics GitHub Actions workflow

.github/workflows/close-topics.yml

@@ -0,0 +1,44 @@
+name: Close Topics
+
+on:
+  # Close Solved closes problem issues with GITHUB_TOKEN, and token-driven
+  # closes never fire `issues` events — so chain off its run instead.
+  # Conclusion is not filtered: the script reconciles state, so running after a
+  # partially successful run is safe and catches whatever it did close.
+  workflow_run:
+    workflows: [Close Solved]
+    types: [completed]
+  # Covers problem issues closed by hand in the UI.
+  issues:
+    types: [closed]
+  workflow_dispatch:
+    inputs:
+      dry_run:
+        description: Report finished topics without closing anything
+        type: boolean
+        default: false
+
+permissions:
+  contents: read
+  issues: write
+
+concurrency:
+  group: close-topics
+  cancel-in-progress: false
+
+jobs:
+  close:
+    # The `issues` trigger fires for every issue in the repo; only closing a
+    # problem sub-issue can ever complete a topic's core set.
+    if: github.event_name != 'issues' || contains(github.event.issue.labels.*.name, 'problem')
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: oven-sh/setup-bun@v2
+
+      # No install step: the script only uses Bun builtins + fetch.
+      - run: bun scripts/close-topics.ts
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          DRY_RUN: ${{ inputs.dry_run }}