Add scheduled RC release workflow

.github/workflows/release-rc.yml

@@ -0,0 +1,74 @@
+name: Schedule RC Release
+
+on:
+  workflow_dispatch:
+  schedule:
+    # Why: GitHub cron uses UTC, not America/Los_Angeles. We trigger at both the
+    # PST and PDT candidate UTC hours, then gate on the actual PT wall clock so
+    # RC releases still happen at 4:00 AM and 3:00 PM PT year-round.
+    - cron: '0 11,12,22,23 * * *'
+
+permissions:
+  contents: write
+
+concurrency:
+  group: release-rc
+  cancel-in-progress: false
+
+jobs:
+  create-rc-tag:
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+
+    steps:
+      - name: Decide whether this schedule should run
+        id: schedule
+        env:
+          EVENT_NAME: ${{ github.event_name }}
+        run: |
+          if [[ "$EVENT_NAME" == "workflow_dispatch" ]]; then
+            echo "should_run=true" >>"$GITHUB_OUTPUT"
+            echo "pt_time=manual" >>"$GITHUB_OUTPUT"
+            exit 0
+          fi
+
+          pt_time=$(TZ=America/Los_Angeles date '+%H:%M')
+          if [[ "$pt_time" != "04:00" && "$pt_time" != "15:00" ]]; then
+            echo "Current PT time is $pt_time; skipping."
+            echo "should_run=false" >>"$GITHUB_OUTPUT"
+            exit 0
+          fi
+
+          echo "should_run=true" >>"$GITHUB_OUTPUT"
+          echo "pt_time=$pt_time" >>"$GITHUB_OUTPUT"
+
+      - name: Checkout
+        if: steps.schedule.outputs.should_run == 'true'
+        uses: actions/checkout@v4
+        with:
+          ref: main
+          fetch-depth: 0
+
+      - name: Setup Node.js
+        if: steps.schedule.outputs.should_run == 'true'
+        uses: actions/setup-node@v4
+        with:
+          node-version: 24
+
+      - name: Configure git author
+        if: steps.schedule.outputs.should_run == 'true'
+        run: |
+          git config user.name "github-actions[bot]"
+          git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
+
+      - name: Sync with latest main
+        if: steps.schedule.outputs.should_run == 'true'
+        run: git pull --ff-only origin main
+
+      - name: Create and push RC tag
+        if: steps.schedule.outputs.should_run == 'true'
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          npm version prerelease --preid=rc
+          git push origin main --follow-tags