feat(docs): add dynamic sitemap.xml route

Generates sitemap from page routes with lastmod from manifest,
priority by section, and monthly changefreq. Fixes 404 referenced
by robots.txt.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: jaysin586

docs/src/routes/sitemap.xml/+server.ts

@@ -0,0 +1,50 @@
+import { env } from '$env/dynamic/public'
+import manifestData from '$lib/sitemap-manifest.json'
+import type { RequestHandler } from '@sveltejs/kit'
+
+const manifest: Record<string, string> = manifestData
+
+const pageFiles = Object.keys(
+    import.meta.glob('/src/routes/**/+page.{svelte,svx,md}', { eager: false })
+)
+
+function toPath(file: string): string {
+    const p = file.replace('/src/routes', '').replace(/\/\+page\.(svelte|svx|md)$/i, '')
+    return p === '' ? '/' : p
+}
+
+function getPriority(path: string): string {
+    if (path === '/') return '1.0'
+    if (path === '/docs/getting-started' || path.startsWith('/docs/api/')) return '0.9'
+    if (path.startsWith('/docs/guides/')) return '0.8'
+    if (path.startsWith('/examples')) return '0.7'
+    return '0.5'
+}
+
+function getChangefreq(path: string): string {
+    if (path === '/') return 'weekly'
+    return 'monthly'
+}
+
+export const GET: RequestHandler = async ({ url }) => {
+    const base = (env.PUBLIC_SITE_URL || `${url.origin}`).replace(/\/$/, '')
+
+    const routes = [...new Set(pageFiles.map(toPath))]
+        .filter((p) => !/\/_(?:.*)|\/(?:\+|__)/.test(p))
+        .sort()
+
+    const today = new Date().toISOString().slice(0, 10)
+    const xml = `<?xml version="1.0" encoding="UTF-8"?>\n<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">\n${routes
+        .map(
+            (p) =>
+                `  <url>\n    <loc>${base}${p}</loc>\n    <lastmod>${manifest[p] || today}</lastmod>\n    <changefreq>${getChangefreq(p)}</changefreq>\n    <priority>${getPriority(p)}</priority>\n  </url>`
+        )
+        .join('\n')}\n</urlset>`
+
+    return new Response(xml, {
+        headers: {
+            'Content-Type': 'application/xml',
+            'Cache-Control': 'max-age=0, s-maxage=3600'
+        }
+    })
+}