ADD thumbnail to database (#12)

* ADD thumbnail to database

* ADD thumbnail generation and retrieval functionality

* ADD thumbnail availability check in VideoCard component

* ADD ClipDTO to reduce exposed internals

* REFactor move APIResponse and VideoMetadata to dto package

* REMOVE unused props from VideoCard

* ADD isThumbnailAvailable function

src/main/resources/db/schema.sql

@@ -23,5 +23,6 @@ CREATE TABLE IF NOT EXISTS clips (
     duration FLOAT NOT NULL,
     file_size FLOAT NOT NULL,
     video_path VARCHAR(255) NOT NULL,
+    thumbnail_path VARCHAR(255) NOT NULL,
     FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE
 );