feat(post-overview): add excludeTag functionality for filtering posts

- Introduced `excludeTag` property in PostOverviewBlockData interface to allow exclusion of specific tag slugs.
- Implemented `excludePostsByTagSlugs` function to filter out posts containing specified tag slugs.
- Updated `resolvePostOverviewBlocks` function to utilize the new exclusion logic, enhancing post filtering capabilities.

src/lib/block-types.ts

@@ -182,6 +182,8 @@ export interface PostOverviewBlockData {
   posts?: unknown[];
   /** Tag-Slugs, nach denen gefiltert wird (nur bei allPosts true). */
   filterByTag?: string[];
+  /** Tag-Slugs, die ausgeschlossen werden (optional, nach filterByTag angewendet). */
+  excludeTag?: string[];
   /** Max. Anzahl Einträge. */
   numberItems?: number;
   /** "list" | "cards". */