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/extractor/mod.rs

@@ -1,5 +1,7 @@
+mod auth;
 mod json;
 mod valid;
 
+pub use auth::AuthUser;
 pub use json::Json;
 pub use valid::Valid;