Assistant checkpoint: Add URL uniqueness constraint and handle duplicates

Assistant generated file changes:
- shared/schema.ts: Add unique constraint to url
- server/storage.ts: Handle duplicate URLs in importNewsletter

---

User prompt:

Keep the id as the primary key but use  the url as an "external id" for the newsletter and don't allow duplicates to be created in the database

server/storage.ts

@@ -43,7 +43,15 @@ export class DatabaseStorage implements IStorage {
   }
 
   async importNewsletter(newsletter: InsertNewsletter): Promise<void> {
-    await db.insert(newsletters).values(newsletter);
+    try {
+      await db.insert(newsletters).values(newsletter);
+    } catch (error: any) {
+      if (error.code === '23505') { // PostgreSQL unique violation code
+        console.log(`Newsletter with URL ${newsletter.url} already exists, skipping`);
+      } else {
+        throw error;
+      }
+    }
   }
 
   async importNewsletters(newNewsletters: InsertNewsletter[]): Promise<void> {

shared/schema.ts

@@ -13,7 +13,7 @@ export const newsletters = pgTable("newsletters", {
   id: serial("id").primaryKey(),
   title: text("title").notNull(),
   date: date("date").notNull(),
-  url: text("url").notNull(),
+  url: text("url").notNull().unique(),
   description: text("description"),
   thumbnail: text("thumbnail"),
   content: text("content"),