🔨 Add Cloudflare Pages docs deploy (parallel to RtD)

.github/workflows/deploy-docs-cf.yml

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+name: Deploy docs to Cloudflare Pages
+
+on:
+  push:
+    branches: [main, master]
+  pull_request:
+    types: [opened, synchronize, reopened]
+  workflow_dispatch:
+
+concurrency:
+  group: deploy-docs-cf-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+jobs:
+  build-and-deploy:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      - uses: astral-sh/setup-uv@08807647e7069bb48b6ef5acd8ec9567f424441b # v8.1.0
+        with:
+          enable-cache: true
+
+      - name: Install dependencies
+        run: uv sync
+
+      - name: Override site_url for the Cloudflare build
+        run: |
+          sed -i 's|^site_url = .*|site_url = "https://owid-docs.pages.dev/"|' zensical.toml
+
+      - name: Build docs
+        run: uv run zensical build --clean
+
+      - name: Add _worker.js (path router for subprojects)
+        run: cp _worker.js site/_worker.js
+
+      - name: Deploy to Cloudflare Pages
+        uses: cloudflare/wrangler-action@v3
+        with:
+          apiToken: ${{ secrets.CLOUDFLARE_API_TOKEN }}
+          accountId: ${{ secrets.CLOUDFLARE_ACCOUNT_ID }}
+          command: >-
+            pages deploy site
+            --project-name=owid-docs
+            --branch=${{ github.head_ref || github.ref_name }}

_worker.js

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+// Cloudflare Pages Functions worker for the owid-docs project.
+//
+// When present at the deployment root, this file intercepts ALL requests
+// for this Pages project. We use it as a thin router so that one custom
+// domain (docs-cf.owid.io and later docs.owid.io) can transparently serve
+// docs from multiple source repos:
+//
+//   /projects/etl/*   →  proxied to https://owid-etl-docs.pages.dev/projects/etl/*
+//   everything else   →  served from this project's own static assets
+//
+// Each subproject keeps its own GitHub repo, its own CI, and its own
+// Pages project (per-PR previews on *.pages.dev still work as today).
+// Add a new route here whenever another subproject migrates to CF Pages.
+
+const SUBPROJECTS = {
+  "/projects/etl/": "https://owid-etl-docs.pages.dev",
+};
+
+export default {
+  async fetch(request, env) {
+    const url = new URL(request.url);
+
+    for (const [prefix, origin] of Object.entries(SUBPROJECTS)) {
+      if (url.pathname.startsWith(prefix)) {
+        const target = `${origin}${url.pathname}${url.search}`;
+        return fetch(target, request);
+      }
+    }
+
+    return env.ASSETS.fetch(request);
+  },
+};