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/feed.rs

@@ -0,0 +1,63 @@
+use super::main::{create_test_user, setup};
+use axum::http::StatusCode;
+use http_body_util::BodyExt;
+use serde_json::json;
+use utils::testing::{make_get_request, make_post_request};
+
+#[tokio::test]
+async fn test_feed_and_user_thoughts() {
+    let app = setup().await;
+    create_test_user(&app.db, "user1").await; // AuthUser is ID 1
+    create_test_user(&app.db, "user2").await;
+    create_test_user(&app.db, "user3").await;
+
+    // As user1, post a thought
+    let body = json!({ "content": "A thought from user1" }).to_string();
+    make_post_request(app.router.clone(), "/thoughts", body).await;
+
+    // As a different "user", create thoughts for user2 and user3 (we cheat here since auth is hardcoded)
+    app::persistence::thought::create_thought(
+        &app.db,
+        2,
+        models::params::thought::CreateThoughtParams {
+            content: "user2 was here".to_string(),
+        },
+    )
+    .await
+    .unwrap();
+    app::persistence::thought::create_thought(
+        &app.db,
+        3,
+        models::params::thought::CreateThoughtParams {
+            content: "user3 checking in".to_string(),
+        },
+    )
+    .await
+    .unwrap();
+
+    // 1. Get thoughts for user2 - should only see their thought
+    let response = make_get_request(app.router.clone(), "/users/user2/thoughts").await;
+    assert_eq!(response.status(), StatusCode::OK);
+    let body = response.into_body().collect().await.unwrap().to_bytes();
+    let v: serde_json::Value = serde_json::from_slice(&body).unwrap();
+    assert_eq!(v["thoughts"].as_array().unwrap().len(), 1);
+    assert_eq!(v["thoughts"][0]["content"], "user2 was here");
+
+    // 2. user1's feed is initially empty
+    let response = make_get_request(app.router.clone(), "/feed").await;
+    assert_eq!(response.status(), StatusCode::OK);
+    let body = response.into_body().collect().await.unwrap().to_bytes();
+    let v: serde_json::Value = serde_json::from_slice(&body).unwrap();
+    assert!(v["thoughts"].as_array().unwrap().is_empty());
+
+    // 3. user1 follows user2
+    make_post_request(app.router.clone(), "/users/user2/follow", "".to_string()).await;
+
+    // 4. user1's feed now has user2's thought
+    let response = make_get_request(app.router.clone(), "/feed").await;
+    assert_eq!(response.status(), StatusCode::OK);
+    let body = response.into_body().collect().await.unwrap().to_bytes();
+    let v: serde_json::Value = serde_json::from_slice(&body).unwrap();
+    assert_eq!(v["thoughts"].as_array().unwrap().len(), 1);
+    assert_eq!(v["thoughts"][0]["author_username"], "user2");
+}