feat: implement user follow/unfollow functionality and thought retrieval by user

- Added follow and unfollow endpoints for users.
- Implemented logic to retrieve thoughts by a specific user.
- Updated user error handling to include cases for already following and not following.
- Created persistence layer for follow relationships.
- Enhanced user and thought schemas to support new features.
- Added tests for follow/unfollow endpoints and thought retrieval.
- Updated frontend to display thoughts and allow posting new thoughts.

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

@@ -26,3 +26,13 @@ pub async fn search_users(db: &DbConn, query: UserQuery) -> Result<Vec<user::Mod
 pub async fn get_user(db: &DbConn, id: i32) -> Result<Option<user::Model>, DbErr> {
     user::Entity::find_by_id(id).one(db).await
 }
+
+pub async fn get_user_by_username(
+    db: &DbConn,
+    username: &str,
+) -> Result<Option<user::Model>, DbErr> {
+    user::Entity::find()
+        .filter(user::Column::Username.eq(username))
+        .one(db)
+        .await
+}