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/videos.ts

@@ -30,6 +30,7 @@ import {
   arrayContains,
   isNull,
   or,
+  ne,
   type SQL,
 } from "drizzle-orm";
 import { requireAdmin } from "../../lib/acl";
@@ -97,6 +98,7 @@ builder.queryField("videos", (t) =>
       sortBy: t.arg.string(),
       duration: t.arg.string(),
       tag: t.arg.string(),
+      excludeId: t.arg.string(),
     },
     resolve: async (_root, args, ctx) => {
       const pageSize = args.limit ?? 24;
@@ -113,6 +115,9 @@ builder.queryField("videos", (t) =>
       if (args.tag) {
         conditions.push(arrayContains(videos.tags, [args.tag]));
       }
+      if (args.excludeId) {
+        conditions.push(ne(videos.id, args.excludeId));
+      }
       if (args.modelId) {
         const videoIds = await ctx.db
           .select({ video_id: video_models.video_id })