fix(landing-page): correct SEO canonical, add robots.txt + favicons (#1061)

The Astro `site` default was `https://open-design.dev`, but the live
Cloudflare Pages deployment is bound to `open-design.ai`. As a result
every `<link rel="canonical">`, `og:url`, and sitemap entry pointed at
the wrong origin, and search engines saw no robots.txt or favicon at
the apex.

- astro.config.ts: switch the default `site` to `https://open-design.ai`
  and document that `OD_LANDING_SITE` stays as the preview-deploy hatch.
- astro.config.ts: filter `/og/` out of the sitemap; that route is the
  1200x630 OG screenshot surface and already carries `noindex`.
- public/robots.txt: allow-all + Disallow `/og/` + canonical sitemap URL.
- public/favicon.svg: 32x32 SVG mark mirroring the on-page `Ø` brand
  glyph (ink ground, paper-stroked italic ellipse, coral slash).
- public/apple-touch-icon.png: 180x180 PNG rendered from the same
  geometry without the rounded corners (iOS applies its own mask).
- index.astro: link `/favicon.svg` (`type="image/svg+xml"`) and
  `/apple-touch-icon.png` from the document head.

Verified locally with `pnpm --filter @open-design/landing-page build`:
the rendered head emits `https://open-design.ai/` for canonical and
`og:url`, the sitemap contains exactly the canonical `/` URL, and the
two `landing-page-deploy.yml` verification scripts (no client JS, >=16
Cloudflare resized image URLs, no local /assets/*.png) still pass.

Co-authored-by: joey <joey@joeydeMacBook-Air.local>
Co-authored-by: Cursor <cursoragent@cursor.com>

apps/landing-page/app/pages/index.astro

@@ -22,6 +22,9 @@ const pageHtml = renderToStaticMarkup(createElement(Page));
     <meta name="description" content={description} />
     <link rel="canonical" href={canonical} />
 
+    <link rel="icon" type="image/svg+xml" href="/favicon.svg" />
+    <link rel="apple-touch-icon" href="/apple-touch-icon.png" />
+
     <meta property="og:type" content="website" />
     <meta property="og:site_name" content="Open Design" />
     <meta property="og:title" content={title} />

apps/landing-page/astro.config.ts

@@ -1,7 +1,15 @@
 import sitemap from '@astrojs/sitemap';
 import { defineConfig } from 'astro/config';
 
-const site = process.env.OD_LANDING_SITE ?? 'https://open-design.dev';
+// Production canonical origin. Used by Astro for `Astro.site`, by
+// `@astrojs/sitemap` for every URL it emits, and by `index.astro` to
+// build the `<link rel="canonical">` / `og:url` tags.
+//
+// `open-design.ai` is the live domain bound to the Cloudflare Pages
+// project (`open-design-landing`); the env override exists so preview
+// builds (Cloudflare Pages preview deployments, local previews on a
+// different host) can stamp their own URL without forking the config.
+const site = process.env.OD_LANDING_SITE ?? 'https://open-design.ai';
 
 export default defineConfig({
   output: 'static',
@@ -9,5 +17,13 @@ export default defineConfig({
   srcDir: './app',
   outDir: './out',
   trailingSlash: 'always',
-  integrations: [sitemap()],
+  integrations: [
+    sitemap({
+      // `/og/` is a screenshot surface for the 1200x630 Open Graph
+      // image — it already carries `<meta name="robots" content="noindex">`
+      // and is `Disallow`-ed from `public/robots.txt`. Filtering it
+      // out of the sitemap keeps the index strictly canonical pages.
+      filter: (page) => !page.includes('/og/'),
+    }),
+  ],
 });

apps/landing-page/public/favicon.svg

@@ -0,0 +1,6 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32" role="img" aria-label="Open Design">
+  <title>Open Design</title>
+  <rect width="32" height="32" rx="6" fill="#14110b"/>
+  <ellipse cx="16" cy="16" rx="6.4" ry="8" fill="none" stroke="#efe7d2" stroke-width="2.4" transform="rotate(-12 16 16)"/>
+  <line x1="9.5" y1="22.5" x2="22.5" y2="9.5" stroke="#ed6f5c" stroke-width="2.4" stroke-linecap="round"/>
+</svg>

apps/landing-page/public/robots.txt

@@ -0,0 +1,14 @@
+# Open Design — landing page (https://open-design.ai/)
+#
+# This file is served verbatim from the apex of the Cloudflare Pages
+# deployment. The sitemap URL must match `astro.config.ts`'s `site`
+# value; @astrojs/sitemap emits the index at `/sitemap-index.xml`.
+User-agent: *
+Allow: /
+
+# The /og/ route is a screenshot surface for the Open Graph image
+# (1200x630). It already carries `<meta name="robots" content="noindex">`
+# but blocking the path here keeps it out of crawl budgets entirely.
+Disallow: /og/
+
+Sitemap: https://open-design.ai/sitemap-index.xml