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/backend/src/graphql/resolvers/articles.ts

@@ -1,7 +1,7 @@
 import { builder } from "../builder";
 import { ArticleType, ArticleListType, AdminArticleListType } from "../types/index";
 import { articles, users } from "../../db/schema/index";
-import { eq, and, lte, desc, asc, ilike, or, count, arrayContains, isNotNull, type SQL } from "drizzle-orm";
+import { eq, and, lte, desc, asc, ilike, or, count, arrayContains, isNotNull, ne, type SQL } from "drizzle-orm";
 import { requireAdmin } from "../../lib/acl";
 import type { DB } from "../../db/connection";
 
@@ -35,6 +35,7 @@ builder.queryField("articles", (t) =>
       offset: t.arg.int(),
       sortBy: t.arg.string(),
       tag: t.arg.string(),
+      excludeId: t.arg.string(),
     },
     resolve: async (_root, args, ctx) => {
       const pageSize = args.limit ?? 24;
@@ -46,6 +47,7 @@ builder.queryField("articles", (t) =>
       }
       if (args.category) conditions.push(eq(articles.category, args.category));
       if (args.tag) conditions.push(arrayContains(articles.tags, [args.tag]));
+      if (args.excludeId) conditions.push(ne(articles.id, args.excludeId));
       if (args.search) {
         conditions.push(
           or(