fix(site): auto-detect Cloudflare Pages build target

Cloudflare Pages' Git integration was building the site with the GitHub
Pages base path '/TermBeam', causing every internal link on
termbeam.pages.dev to 404 (and Cloudflare to fall back to a redirect to
the github.io copy).

astro.config.mjs now auto-detects CF builds via the CF_PAGES=1 env var
that Cloudflare sets during builds, switching to base '/' and using
CF_PAGES_URL for canonical/OG metadata. GitHub Pages builds remain
unchanged. Cloudflare's project just needs:
  Root directory: packages/site
  Build command: npm run build
  Output directory: dist

Removes the redundant GH Actions Cloudflare workflow now that Cloudflare's
own Git integration handles deploys automatically.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: dorlugasigal

.github/workflows/cloudflare-pages.yml

@@ -3,13 +3,15 @@ import { defineConfig } from 'astro/config';
 import starlight from '@astrojs/starlight';
 
 // Build target is driven by env so the same source can ship to multiple hosts:
-//   DEPLOY_TARGET=github-pages  (default) — base /TermBeam, site dorlugasigal.github.io
-//   DEPLOY_TARGET=cloudflare              — base /, site from SITE_URL or termbeam.dev
-const target = process.env.DEPLOY_TARGET || 'github-pages';
-const isCF = target === 'cloudflare';
+//   default: GitHub Pages — base /TermBeam, site dorlugasigal.github.io
+//   Cloudflare Pages: detected automatically via CF_PAGES=1 (set by Cloudflare's
+//     Git integration during builds) OR explicitly via DEPLOY_TARGET=cloudflare.
+//     Base /, site from CF_PAGES_URL (set by Cloudflare) or SITE_URL.
+const explicitTarget = process.env.DEPLOY_TARGET;
+const isCF = explicitTarget === 'cloudflare' || process.env.CF_PAGES === '1';
 
 const site = isCF
-  ? process.env.SITE_URL || 'https://termbeam.dev'
+  ? process.env.SITE_URL || process.env.CF_PAGES_URL || 'https://termbeam.pages.dev'
   : 'https://dorlugasigal.github.io';
 const base = isCF ? '/' : '/TermBeam';
 const ogImage = `${site.replace(/\/$/, '')}${base === '/' ? '' : base}/og-image.png`;