fix: remove trailing slash from slugs to fix Ghost API lookup

- Strip trailing slashes from slugs in get_slug() function
- This prevents double slashes in the Ghost API URL which was causing
  get_existing_post_id() to fail and create duplicate posts

ghost-upload/src/main.rs

@@ -143,7 +143,7 @@ impl Post {
 }
 
 fn get_slug(link: &str) -> String {
-    link.split_once("/posts/").unwrap().1.to_string()
+    link.split_once("/posts/").unwrap().1.trim_end_matches('/').to_string()
 }
 
 async fn extract_article_content(original_link: &str) -> String {