Add sponsored content filtering for articles

Adds a new `isSponsored` boolean field to the `articles` table in `shared/schema.ts` to allow for filtering sponsored articles. Includes several generated image files for advertisement purposes.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 0fb68265-c270-4198-9584-3d9be9bddb41
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shared/schema.ts

@@ -66,6 +66,7 @@ export const articles = pgTable("articles", {
   tags: text("tags").array(),
   isPinned: boolean("is_pinned").default(false),
   isFeatured: boolean("is_featured").default(false),
+  isSponsored: boolean("is_sponsored").default(false),
   publishedMinutesAgo: integer("published_minutes_ago").notNull().default(sql`1 + floor(random() * 59)::int`),
   publishedAt: timestamp("published_at").defaultNow(),
   createdAt: timestamp("created_at").defaultNow(),