feat(website): add SEO, sitemap, redirects, CI workflow, and Vercel config (#10156)

## Summary

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## Changes

- **What**: <!-- Core functionality added/modified -->
- **Breaking**: <!-- Any breaking changes (if none, remove this line)
-->
- **Dependencies**: <!-- New dependencies (if none, remove this line)
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## Review Focus

<!-- Critical design decisions or edge cases that need attention -->

<!-- If this PR fixes an issue, uncomment and update the line below -->
<!-- Fixes #ISSUE_NUMBER -->

## Screenshots (if applicable)

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┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-10156-feat-website-add-SEO-sitemap-redirects-CI-workflow-and-Vercel-config-3266d73d3650816ab9eaebd11072d481)
by [Unito](https://www.unito.io)

---------

Co-authored-by: GitHub Action <action@github.com>

.github/workflows/ci-website-build.yaml

@@ -0,0 +1,33 @@
+# Description: Build and validate the marketing website (apps/website)
+name: 'CI: Website Build'
+
+on:
+  push:
+    branches: [main, master, website/*]
+    paths:
+      - 'apps/website/**'
+      - 'packages/design-system/**'
+      - 'pnpm-lock.yaml'
+  pull_request:
+    branches-ignore: [wip/*, draft/*, temp/*]
+    paths:
+      - 'apps/website/**'
+      - 'packages/design-system/**'
+      - 'pnpm-lock.yaml'
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v6
+
+      - name: Setup frontend
+        uses: ./.github/actions/setup-frontend
+
+      - name: Build website
+        run: pnpm --filter @comfyorg/website build