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/tests/api/main.rs

@@ -0,0 +1,29 @@
+use api::setup_router;
+use app::persistence::user::create_user;
+use axum::Router;
+use models::params::user::CreateUserParams;
+use sea_orm::DatabaseConnection;
+use utils::testing::setup_test_db;
+
+pub struct TestApp {
+    pub router: Router,
+    pub db: DatabaseConnection,
+}
+
+pub async fn setup() -> TestApp {
+    let db = setup_test_db("sqlite::memory:")
+        .await
+        .expect("Failed to set up test db");
+    let router = setup_router(db.clone());
+    TestApp { router, db }
+}
+
+// Helper to create users for tests
+pub async fn create_test_user(db: &DatabaseConnection, username: &str) {
+    let params = CreateUserParams {
+        username: username.to_string(),
+    };
+    create_user(db, params)
+        .await
+        .expect("Failed to create test user");
+}