perf: review-fixes (N+1, waterfalls, sanitize-cache, lazy strommix)

- blog-utils.resolvePostOverviewBlocks: parallel getPostBySlug via
  Promise.all + .catch(null) instead of sequential await loop.
- blog-utils.resolveCalendarBlocks: same fix for calendar items.
- [...slug] page load: SearchableText/Calendar/DeadlineBanner now run
  parallel after tagsMap (was strict waterfall).
- sanitize-blocks: LRU cache keyed on raw html input — sanitize-html is
  ~ms/KB, the same content repeats across pages and cache hits.
- cms.getNormalizedTranslations: WeakMap-memoised the per-request
  Object.entries normalize loop on top of the existing 5-min bundle TTL.
- cms.cached: opt-in dev cache via DEV_CACHE_CMS=1 (default still off).
- rusty-image.ensureTransformedImage: was async-wrapping a sync URL
  builder; made sync, removed awaits at call sites — saves microtasks.
- BlockRenderer: lazy-load StrommixBlock (~220 KB) via dynamic import
  in the template — pages without the live-strommix widget no longer
  ship its bundle.

Also: enabled Caddy zstd+gzip on windwiderstand.de vhost (server-side
edit; verified `content-encoding: zstd` on response).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/hooks.server.ts

@@ -1,4 +1,4 @@
-import { getTranslationBundleBySlug } from '$lib/cms';
+import { getNormalizedTranslations } from '$lib/cms';
 import { isCmsAvailable } from '$lib/cms-health.server';
 import { maintenanceResponse } from '$lib/maintenance.server';
 import { TRANSLATION_BUNDLE_SLUG } from '$lib/constants';
@@ -97,23 +97,10 @@ export const handle: Handle = async ({ event, resolve }) => {
   }
 
   try {
-    const bundle = await getTranslationBundleBySlug(TRANSLATION_BUNDLE_SLUG, { locale: 'de' });
-    if (bundle?.strings && typeof bundle.strings === 'object') {
-      const normalized: Record<string, string> = {};
-      for (const [key, val] of Object.entries(bundle.strings)) {
-        const v = val as unknown;
-        const str =
-          typeof v === 'string'
-            ? v
-            : typeof v === 'object' && v !== null && 'value' in v
-              ? (v as { value?: unknown }).value
-              : (v as { text?: unknown })?.text ?? (v as { label?: unknown })?.label;
-        if (typeof str === 'string') normalized[key] = str;
-      }
-      event.locals.translations = normalized;
-    } else {
-      event.locals.translations = {};
-    }
+    event.locals.translations = await getNormalizedTranslations(
+      TRANSLATION_BUNDLE_SLUG,
+      { locale: 'de' },
+    );
   } catch (err) {
     event.locals.translations = {};
     logWarn('hooks.translations', err);