feat(youtube): playlist support + URL parsing in youtube_video block

YoutubeVideoBlockData gains an optional `playlistId`. The block now
accepts either a video, a playlist, or both, and either field can be
filled with a raw ID *or* a full youtube.com / youtu.be URL — a
helper extracts the ?v= and ?list= parameters automatically.

Embed routing:
- video only           → /embed/<id>?rel=0
- playlist only        → /embed/videoseries?list=<plid>&rel=0
- video + playlist     → /embed/<id>?list=<plid>&rel=0
- block.params merged  via URLSearchParams

Also tweaks ImageGalleryBlock (grid variant): green padding/contain
fit, darker caption gradient, smaller left-aligned label that expands
on hover. Hides post_overview block when no posts and no intro text
(prevents a bare heading on /mediathek).

src/lib/block-types.ts

@@ -155,6 +155,13 @@ export interface YoutubeVideoBlockData {
   _type?: "youtube_video";
   _slug?: string;
   youtubeId?: string;
+  /**
+   * Playlist-ID (PLxxxxx). Wenn ohne youtubeId gesetzt, lädt die Playlist
+   * von vorne; mit youtubeId startet das Video in der Playlist.
+   * Akzeptiert auch direkte URLs wie
+   * https://www.youtube.com/watch?v=...&list=PL... (wird parsed).
+   */
+  playlistId?: string;
   title?: string;
   description?: string;
   params?: string;

src/lib/components/blocks/ImageGalleryBlock.svelte

@@ -176,7 +176,7 @@
         <li class="m-0 p-0">
           <button
             type="button"
-            class="group relative block w-full aspect-square overflow-hidden rounded-sm bg-stein-100 cursor-zoom-in focus:outline-none focus:ring-2 focus:ring-wald-500"
+            class="group relative block w-full aspect-square overflow-hidden rounded-sm bg-wald-100 p-2 cursor-zoom-in focus:outline-none focus:ring-2 focus:ring-wald-500"
             onclick={() => openModal(i)}
             aria-label={label || t(T.image_gallery_open_aria)}
           >
@@ -185,15 +185,15 @@
               focal={item.focal}
               width={400}
               aspect="1/1"
-              fit="cover"
-              quality={75}
+              fit="contain"
+              quality={80}
               alt={label}
-              class="w-full h-full object-cover transition-transform duration-300 group-hover:scale-105"
+              class="w-full h-full object-contain transition-transform duration-300 group-hover:scale-105"
               loading={i < 4 ? "eager" : "lazy"}
             />
             {#if label}
               <span
-                class="absolute inset-x-0 bottom-0 px-2 py-1.5 text-xs text-white bg-gradient-to-t from-black/70 via-black/40 to-transparent opacity-0 transition-opacity duration-200 group-hover:opacity-100 group-focus:opacity-100 line-clamp-2"
+                class="absolute inset-x-0 bottom-0 max-h-full overflow-y-auto px-2 py-1.5 text-left text-[10px] leading-tight text-white bg-gradient-to-t from-black/95 via-black/80 to-black/30 opacity-0 transition-opacity duration-200 group-hover:opacity-100 group-focus:opacity-100 line-clamp-2 group-hover:line-clamp-none group-focus:line-clamp-none"
               >
                 {label}
               </span>

src/lib/components/blocks/YoutubeVideoBlock.svelte

@@ -7,16 +7,85 @@
   const t = useTranslate();
   let { block }: { block: YoutubeVideoBlockData } = $props();
 
+  /**
+   * Liefert (videoId, playlistId) — beide Felder akzeptieren auch volle
+   * youtube.com-URLs (watch?v=…&list=…, /playlist?list=…) statt reiner IDs.
+   */
+  function parseYouTube(input: string | undefined): {
+    videoId: string | null;
+    playlistId: string | null;
+  } {
+    if (!input) return { videoId: null, playlistId: null };
+    const raw = input.trim();
+    if (!raw) return { videoId: null, playlistId: null };
+    // Direkte URL erkennen.
+    if (raw.startsWith("http")) {
+      try {
+        const u = new URL(raw);
+        const v = u.searchParams.get("v");
+        const list = u.searchParams.get("list");
+        // youtu.be/<id> → path
+        let pathVid: string | null = null;
+        if (u.hostname.includes("youtu.be")) {
+          pathVid = u.pathname.replace(/^\/+/, "").split("/")[0] || null;
+        }
+        // /embed/<id>
+        const embedMatch = u.pathname.match(/\/embed\/([^/?]+)/);
+        const embedVid = embedMatch?.[1] ?? null;
+        return {
+          videoId: v ?? pathVid ?? embedVid,
+          playlistId: list,
+        };
+      } catch {
+        return { videoId: null, playlistId: null };
+      }
+    }
+    // Reine ID: PL... → Playlist, sonst Video.
+    if (/^PL[A-Za-z0-9_-]+$/.test(raw)) {
+      return { videoId: null, playlistId: raw };
+    }
+    return { videoId: raw, playlistId: null };
+  }
+
+  const parsed = $derived.by(() => {
+    const fromVid = parseYouTube(block.youtubeId);
+    const fromList = parseYouTube(block.playlistId);
+    return {
+      videoId: fromVid.videoId ?? fromList.videoId,
+      // Explizites playlistId-Feld gewinnt; sonst aus youtubeId-URL.
+      playlistId: fromList.playlistId ?? fromVid.playlistId,
+    };
+  });
+
   const layoutClasses = $derived(getBlockLayoutClasses(block.layout));
-  const embedUrl = $derived(
-    block.youtubeId
-      ? `https://www.youtube-nocookie.com/embed/${encodeURIComponent(block.youtubeId)}?rel=0${block.params ? `&${String(block.params).replace(/^&/, "")}` : ""}`
-      : null,
-  );
+
+  const embedUrl = $derived.by(() => {
+    const { videoId, playlistId } = parsed;
+    if (!videoId && !playlistId) return null;
+    const base = "https://www.youtube-nocookie.com/embed";
+    const path = videoId
+      ? `/${encodeURIComponent(videoId)}`
+      : "/videoseries";
+    const params = new URLSearchParams();
+    params.set("rel", "0");
+    if (playlistId) params.set("list", playlistId);
+    // Block-eigene `params` als Query-String mergen (z.B. "start=42&autoplay=0").
+    if (block.params) {
+      try {
+        const extra = new URLSearchParams(String(block.params).replace(/^&/, ""));
+        for (const [k, v] of extra.entries()) params.set(k, v);
+      } catch {
+        /* ignore malformed params */
+      }
+    }
+    return `${base}${path}?${params.toString()}`;
+  });
+
+  const hasEmbed = $derived(embedUrl != null);
 </script>
 
 <div class={layoutClasses} data-block-type="youtube_video" data-block-slug={block._slug}>
-  {#if block.youtubeId}
+  {#if hasEmbed}
     <div class="aspect-video w-full overflow-hidden rounded-sm bg-stein-100">
       <iframe
         title={block.title ?? t(T.youtube_title_fallback)}