docs: add Astro Starlight docs site with GitHub Pages deployment

7-page docs site: Overview, Getting Started, DataFrame API, Operators,
Formats, Architecture, Deployment. Built with Astro + Starlight, deployed
to GitHub Pages via docs.yml workflow on push to docs/.

Author: teamchong

.github/workflows/docs.yml

@@ -0,0 +1,36 @@
+name: Deploy Docs
+
+on:
+  push:
+    branches: [main]
+    paths: [docs/**]
+  workflow_dispatch:
+
+permissions:
+  pages: write
+  id-token: write
+
+concurrency:
+  group: pages
+  cancel-in-progress: false
+
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+    environment: github-pages
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22
+
+      - run: cd docs && npm ci
+
+      - run: cd docs && npx astro build
+
+      - uses: actions/upload-pages-artifact@v3
+        with:
+          path: docs/dist
+
+      - uses: actions/deploy-pages@v4

docs/.gitignore

@@ -0,0 +1,3 @@
+node_modules/
+dist/
+.astro/

docs/astro.config.mjs

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+import { defineConfig } from "astro/config";
+import starlight from "@astrojs/starlight";
+
+export default defineConfig({
+  site: "https://teamchong.github.io",
+  base: "/querymode",
+  integrations: [
+    starlight({
+      title: "querymode",
+      social: [
+        {
+          icon: "github",
+          label: "GitHub",
+          href: "https://github.com/teamchong/querymode",
+        },
+      ],
+      sidebar: [
+        { label: "Overview", slug: "index" },
+        { label: "Getting Started", slug: "getting-started" },
+        { label: "DataFrame API", slug: "dataframe-api" },
+        { label: "Operators", slug: "operators" },
+        { label: "Formats", slug: "formats" },
+        { label: "Architecture", slug: "architecture" },
+        { label: "Deployment", slug: "deployment" },
+      ],
+    }),
+  ],
+});