feat: Refactor user and thought models to use UUIDs instead of integers

- Updated user and thought models to utilize UUIDs for primary keys.
- Modified persistence functions to accommodate UUIDs for user and thought IDs.
- Implemented tag functionality with new Tag and ThoughtTag models.
- Added migration scripts to create new tables for tags and thought-tag relationships.
- Enhanced thought creation to parse hashtags and link them to thoughts.
- Updated tests to reflect changes in user and thought ID types.

thoughts-backend/tests/app/persistence/user.rs

@@ -14,6 +14,5 @@ pub(super) async fn test_user(db: &DatabaseConnection) {
         .try_into_model() // Convert ActiveModel to Model for easier checks
         .unwrap();
 
-    assert_eq!(user_model.id, 1);
     assert_eq!(user_model.username, "test");
 }