feat(image): enhance image handling with new properties and responsive support

- Updated PostEntry type to include _rawImageUrl and _imageFocal for improved image management.
- Refactored image handling in various components to utilize the new properties, ensuring better focal point support and responsive image rendering.
- Introduced warmResponsiveImage function for pre-fetching image variants to optimize loading performance.
- Replaced CmsImage component with RustyImage in multiple blocks for consistent image processing.

src/lib/components/blocks/ImageBlock.svelte

@@ -1,30 +1,16 @@
 <script lang="ts">
   import { getBlockLayoutClasses } from "$lib/block-layout";
   import type { ImageBlockData } from "$lib/block-types";
-  import CmsImage from "$lib/components/CmsImage.svelte";
+  import RustyImage from "$lib/components/RustyImage.svelte";
+  import { extractCmsImageField } from "$lib/rusty-image";
 
   let { block }: { block: ImageBlockData } = $props();
 
-  /** Rohe Bild-Quelle für /cms-images (URL, //-URL oder Asset-Dateiname/Slug). */
-  function getRawSrc(b: ImageBlockData): string | null {
-    const img = b.img ?? b.image;
-    if (typeof img === "string") {
-      const s = img.trim();
-      if (!s) return null;
-      return s.startsWith("//") ? `https:${s}` : s;
-    }
-    if (img && typeof img === "object") {
-      const src =
-        (img as { src?: string }).src ?? (img as { file?: { url?: string } }).file?.url;
-      if (typeof src === "string" && src)
-        return src.startsWith("//") ? `https:${src}` : src;
-    }
-    return null;
-  }
-
   const layoutClasses = $derived(getBlockLayoutClasses(block.layout));
   const imageSource = $derived(block.image ?? block.img);
-  const rawSrc = $derived(getRawSrc(block));
+  const imageField = $derived(extractCmsImageField(imageSource));
+  const rawSrc = $derived(imageField?.url ?? null);
+  const focal = $derived(imageField?.focal ?? null);
   $effect(() => {
     if (!rawSrc && block._slug) {
       console.warn("[ImageBlock] Bild nicht verfügbar:", block._slug, {
@@ -57,10 +43,10 @@
 <div class={layoutClasses} data-block-type="image" data-block-slug={block._slug}>
   {#if rawSrc}
     <figure class="max-w-[400px]">
-      <CmsImage
+      <RustyImage
         src={rawSrc}
+        focal={focal}
         width={800}
-        format="webp"
         quality={85}
         fit="contain"
         alt={block.caption ?? title ?? ""}