seo: enforce trailing slash on all URLs

- Set trailingSlash='always' globally via root layout.
- Update postHref, pageHref, Pagination, tag/breadcrumb hrefs, blog→posts
  redirects to emit trailing slash.
- Match old Astro canonical so indexed URLs hit 200 directly instead of
  308-redirect.

src/routes/+layout.server.ts

@@ -1,4 +1,7 @@
 import type { LayoutServerLoad } from './$types';
+
+export const trailingSlash = 'always';
+
 import {
   getNavigationByKey,
   NavigationKeys,
@@ -71,7 +74,7 @@ export const load: LayoutServerLoad = async ({ locals }) => {
     for (const p of posts) {
       const label = p.linkName ?? p.headline ?? p.slug ?? p._slug ?? '';
       const urlSlug = normalizeSlug(p.slug ?? p._slug);
-      const canonical = urlSlug ? `/post/${encodeURIComponent(urlSlug)}` : '';
+      const canonical = urlSlug ? `/post/${encodeURIComponent(urlSlug)}/` : '';
       const keySlug = normalizeSlug(p.slug);
       const keyUnderscore = normalizeSlug(p._slug);
       if (keySlug) {
@@ -111,7 +114,8 @@ export const load: LayoutServerLoad = async ({ locals }) => {
               .split('/')
               .filter(Boolean)
               .map((seg) => encodeURIComponent(seg))
-              .join('/');
+              .join('/') +
+            '/';
       const href = postHref ?? pageHref;
       headerLinks.push({ href, label });
     }

src/routes/api/search-index/+server.ts

@@ -25,7 +25,7 @@ export type SearchHit = {
 function pageHref(p: { slug?: string; _slug?: string }): string {
   const raw = (p.slug ?? p._slug ?? '').replace(/^\//, '').trim();
   if (!raw || raw === 'home') return '/';
-  return '/' + raw.split('/').filter(Boolean).map(encodeURIComponent).join('/');
+  return '/' + raw.split('/').filter(Boolean).map(encodeURIComponent).join('/') + '/';
 }
 
 export const GET: RequestHandler = async () => {

src/routes/blog/page/[page]/+page.server.ts

@@ -2,5 +2,5 @@ import type { PageServerLoad } from './$types';
 import { redirect } from '@sveltejs/kit';
 
 export const load: PageServerLoad = async ({ params }) => {
-  redirect(301, `/posts/page/${encodeURIComponent(params.page)}`);
+  redirect(301, `/posts/page/${encodeURIComponent(params.page)}/`);
 };

src/routes/blog/tag/[tag]/+page.server.ts

@@ -2,5 +2,5 @@ import type { PageServerLoad } from './$types';
 import { redirect } from '@sveltejs/kit';
 
 export const load: PageServerLoad = async ({ params }) => {
-  redirect(301, `/posts/tag/${encodeURIComponent(params.tag)}`);
+  redirect(301, `/posts/tag/${encodeURIComponent(params.tag)}/`);
 };

src/routes/post/[slug]/+page.server.ts

@@ -121,7 +121,7 @@ export const load: PageServerLoad = async ({ params, locals, url }) => {
     socialImage: postImageUrl ?? undefined,
     breadcrumbItems: [
       { href: '/', label: 'Start' },
-      { href: '/posts', label: 'Beiträge' },
+      { href: '/posts/', label: 'Beiträge' },
       { label: post.headline ?? post.linkName ?? post.slug ?? post._slug ?? slug },
     ],
   };

src/routes/posts/tag/[tag]/+page.server.ts

@@ -13,7 +13,7 @@ export const load: PageServerLoad = async ({ params, locals }) => {
     seoDescription: `Beiträge zum Thema ${result.tagName}.`,
     breadcrumbItems: [
       { href: '/', label: t(translations, T.nav_start) },
-      { href: '/posts', label: t(translations, T.nav_posts) },
+      { href: '/posts/', label: t(translations, T.nav_posts) },
       { label: result.tagName ?? '' },
     ],
   };

src/routes/posts/tag/[tag]/page/[page]/+page.server.ts

@@ -14,8 +14,8 @@ export const load: PageServerLoad = async ({ params, locals }) => {
     seoDescription: `Beiträge zum Thema ${result.tagName}.`,
     breadcrumbItems: [
       { href: '/', label: t(translations, T.nav_start) },
-      { href: '/posts', label: t(translations, T.nav_posts) },
-      { href: `/posts/tag/${encodeURIComponent(params.tag)}`, label: result.tagName ?? '' },
+      { href: '/posts/', label: t(translations, T.nav_posts) },
+      { href: `/posts/tag/${encodeURIComponent(params.tag)}/`, label: result.tagName ?? '' },
     ],
   };
 };

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

@@ -15,7 +15,8 @@ function pageHref(canonical: string): string {
       .split('/')
       .filter(Boolean)
       .map((seg) => encodeURIComponent(seg))
-      .join('/')
+      .join('/') +
+    '/'
   );
 }
 
@@ -40,8 +41,8 @@ export const GET: RequestHandler = async ({ url }) => {
 
   const urls: { loc: string; lastmod?: string; changefreq?: string; priority?: string }[] = [
     { loc: `${site}/`, changefreq: 'daily', priority: '1.0' },
-    { loc: `${site}/posts`, changefreq: 'daily', priority: '0.8' },
-    { loc: `${site}/blog`, changefreq: 'daily', priority: '0.8' },
+    { loc: `${site}/posts/`, changefreq: 'daily', priority: '0.8' },
+    { loc: `${site}/blog/`, changefreq: 'daily', priority: '0.8' },
   ];
 
   try {