feat: related content and featured cross-content sidebar widgets

- Add excludeId arg to videos and articles GraphQL resolvers
- Add excludeId + featured params to getVideos/getArticles services
- Video page: fetch related videos by tag + featured article in parallel
- Article page: fetch related articles by category + featured video in parallel
- Implement sidebar widgets with thumbnails, metadata, hover interactions
- Add videos.related and magazine.related i18n keys
- Seed dummy articles (spotlight, interview, psychology) and videos with
  overlapping tags for testing related content

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

packages/frontend/src/lib/services.ts

@@ -245,6 +245,7 @@ const ARTICLES_QUERY = gql`
     $limit: Int
     $featured: Boolean
     $tag: String
+    $excludeId: String
   ) {
     articles(
       search: $search
@@ -254,6 +255,7 @@ const ARTICLES_QUERY = gql`
       limit: $limit
       featured: $featured
       tag: $tag
+      excludeId: $excludeId
     ) {
       items {
         id
@@ -287,6 +289,7 @@ export async function getArticles(
     limit?: number;
     featured?: boolean;
     tag?: string;
+    excludeId?: string;
   } = {},
   fetchFn?: typeof globalThis.fetch,
 ): Promise<{ items: Article[]; total: number }> {
@@ -366,6 +369,7 @@ const VIDEOS_QUERY = gql`
     $sortBy: String
     $duration: String
     $tag: String
+    $excludeId: String
   ) {
     videos(
       modelId: $modelId
@@ -376,6 +380,7 @@ const VIDEOS_QUERY = gql`
       sortBy: $sortBy
       duration: $duration
       tag: $tag
+      excludeId: $excludeId
     ) {
       items {
         id
@@ -416,6 +421,8 @@ export async function getVideos(
     offset?: number;
     limit?: number;
     tag?: string;
+    featured?: boolean;
+    excludeId?: string;
   } = {},
   fetchFn?: typeof globalThis.fetch,
 ): Promise<{ items: Video[]; total: number }> {