Add daily sweep to enforce issue lifecycle label timeouts

Introduce a simple, mechanical daily sweep that closes issues with
lifecycle labels past their timeout:

- needs-repro: 7 days
- needs-info: 7 days
- needs-votes: 30 days
- stale: 30 days

The sweep checks when the label was last applied via the events API,
and closes the issue if the timeout has elapsed. No AI, no comment
checking — if the label is still there past its timeout, close it.
Removing a label (by a triager, slash command, or future AI retriage)
is what prevents closure.

Each close message directs the reporter to open a new issue rather
than engaging with the closed one.

The script supports --dry-run for local testing:
  GITHUB_TOKEN=$(gh auth token) \
  GITHUB_REPOSITORY_OWNER=anthropics \
  GITHUB_REPOSITORY_NAME=claude-code \
  bun run scripts/sweep.ts --dry-run

## Test plan

Ran --dry-run against anthropics/claude-code. Correctly identified 3
issues past their timeouts (1 needs-repro at 12d, 2 needs-info at
14d and 26d). No false positives.

.github/workflows/sweep.yml

@@ -0,0 +1,31 @@
+name: "Daily Issue Sweep"
+
+on:
+  schedule:
+    - cron: "0 10 * * *" # 2am Pacific
+  workflow_dispatch:
+
+permissions:
+  issues: write
+
+concurrency:
+  group: daily-issue-sweep
+
+jobs:
+  sweep:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Setup Bun
+        uses: oven-sh/setup-bun@v2
+        with:
+          bun-version: latest
+
+      - name: Enforce lifecycle timeouts
+        run: bun run scripts/sweep.ts
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          GITHUB_REPOSITORY_OWNER: ${{ github.repository_owner }}
+          GITHUB_REPOSITORY_NAME: ${{ github.event.repository.name }}