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/api/src/routers/mod.rs

@@ -1,15 +1,21 @@
 use axum::Router;
 
+pub mod feed;
 pub mod root;
+pub mod thought;
 pub mod user;
 
 use app::state::AppState;
 use root::create_root_router;
 use user::create_user_router;
 
+use crate::routers::{feed::create_feed_router, thought::create_thought_router};
+
 pub fn create_router(state: AppState) -> Router {
     Router::new()
         .merge(create_root_router())
         .nest("/users", create_user_router())
+        .nest("/thoughts", create_thought_router())
+        .nest("/feed", create_feed_router())
         .with_state(state)
 }