feat(security+obs): SSRF allowlist, HTML sanitization, timing-safe tokens, fetch timeouts, structured logger

Security:
  - cms-images / cms-files now share resolveCmsSource (cms-source.server.ts)
    which enforces an allowlist: asset filename, absolute path on the CMS
    host, or full URL exact-matching the configured CMS host+protocol.
    Foreign hosts, protocol-relative URLs and path traversal return 400.
  - markdown-safe.ts is the single configured marked entrypoint; it
    disables raw HTML rendering globally (renderer.html() returns ''),
    removing the inline script/iframe injection vector via markdown.
    All 8 marked imports across components and loaders now go through it.
  - sanitize-blocks.server.ts walks resolved page/post content and runs
    HtmlBlock html fields through sanitize-html with a tight allowlist
    (no script/style/on*, only youtube/vimeo/spotify iframes, mailto/tel
    plus http(s) schemes, target=_blank gets rel=noopener).
  - Webhook tokens (revalidate, cache/clear) compared via
    crypto.timingSafeEqual through auth-token.server.ts.
  - cms.ts wraps every fetch in cmsFetch(): 5 s default timeout via
    AbortSignal.timeout, override per call or globally via
    PUBLIC_CMS_FETCH_TIMEOUT_MS. Stops slow CMS responses from pinning
    SSR workers indefinitely.

Observability:
  - log.server.ts gives logWarn / logError / logInfo with scope + context;
    swallowed catch {} blocks in hooks, layout.server, +page.server,
    [...slug]/+page.server and sitemap now log instead of going silent.

Routing:
  - Legacy /blog, /blog/page/:n, /blog/tag/:t and /p/:slug stub routes
    deleted; their 301 redirects moved into hooks.server.ts so the
    request never enters the SvelteKit page pipeline.

Tests (vitest, server-side):
  - auth-token.server.test.ts (6 cases for constant-time compare)
  - cms-source.server.test.ts  (8 cases for SSRF allowlist)
  - sanitize-blocks.server.test.ts (9 cases for sanitizer + walker)
  All 23 green.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/routes/+page.server.ts

@@ -13,6 +13,8 @@ import {
   resolveDeadlineBannerBlocks,
 } from '$lib/blog-utils';
 import { DEFAULT_HOME_PAGE_SLUG, PAGE_RESOLVE, SITE_NAME } from '$lib/constants';
+import { sanitizeBlocks } from '$lib/sanitize-blocks.server';
+import { logWarn } from '$lib/log.server';
 
 const BANNER_WIDTHS = [640, 960, 1280, 1600, 1920];
 const BANNER_AR = '16/9';
@@ -27,8 +29,8 @@ export const load: PageServerLoad = async ({ locals, fetch }) => {
   let homeSlug = DEFAULT_HOME_PAGE_SLUG;
   try {
     homeSlug = (await getHomePageSlugFromConfig({ locale: 'de' })) ?? DEFAULT_HOME_PAGE_SLUG;
-  } catch {
-    // fallback
+  } catch (err) {
+    logWarn('home.slug', err);
   }
 
   let page = null;
@@ -47,9 +49,10 @@ export const load: PageServerLoad = async ({ locals, fetch }) => {
       await resolveSearchableTextBlocks(page, tagsMap);
       await resolveCalendarBlocks(page);
       await resolveDeadlineBannerBlocks(page);
+      sanitizeBlocks(page);
     }
-  } catch {
-    // CMS nicht erreichbar
+  } catch (err) {
+    logWarn('home.page', err, { homeSlug });
   }
 
   const siteName = (import.meta.env.PUBLIC_SITE_NAME as string | undefined) || SITE_NAME;