Add newsletter send workflows (test pool + real pool)

scripts/send-newsletter.mjs sends newsletter/<issue>/index.html via the
Resend batch API (100/batch, paced under the 10 req/s team limit, retries
rate-limit 429s/5xx, idempotency keys so re-runs resume without dupes) to
the active subscribers of a pool fetched with the scoped send key.
Adds one-click List-Unsubscribe headers. Never logs subscriber emails.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.github/workflows/newsletter-send.yml

@@ -0,0 +1,36 @@
+name: "Newsletter: SEND to subscribers (pool apophenia)"
+
+on:
+  workflow_dispatch:
+    inputs:
+      issue:
+        description: "Issue dir under newsletter/ (e.g. issue-2026.10.07). Sends to ALL subscribers."
+        required: true
+        type: string
+
+permissions:
+  contents: read
+
+# Never run two real sends at once
+concurrency:
+  group: newsletter-send
+  cancel-in-progress: false
+
+jobs:
+  send:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+
+      - name: Send to pool "apophenia"
+        run: node scripts/send-newsletter.mjs
+        env:
+          ISSUE: ${{ inputs.issue }}
+          POOL: apophenia
+          RESEND_API_KEY: ${{ secrets.RESEND_API_KEY }}
+          NEWSLETTER_SEND_KEY: ${{ secrets.NEWSLETTER_SEND_KEY }}
+          NEWSLETTER_FROM: ${{ secrets.NEWSLETTER_FROM }}

.github/workflows/newsletter-test.yml

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+name: "Newsletter: test send (pool test)"
+
+on:
+  workflow_dispatch:
+    inputs:
+      issue:
+        description: "Issue dir under newsletter/ (e.g. issue-2026.10.07)"
+        required: true
+        type: string
+
+permissions:
+  contents: read
+
+jobs:
+  send:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+
+      - name: Send to pool "test"
+        run: node scripts/send-newsletter.mjs
+        env:
+          ISSUE: ${{ inputs.issue }}
+          POOL: test
+          SUBJECT_PREFIX: "[TEST] "
+          RESEND_API_KEY: ${{ secrets.RESEND_API_KEY }}
+          NEWSLETTER_SEND_KEY: ${{ secrets.NEWSLETTER_SEND_KEY }}
+          NEWSLETTER_FROM: ${{ secrets.NEWSLETTER_FROM }}