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/models/src/params/thought.rs

@@ -4,8 +4,10 @@ use validator::Validate;
 
 #[derive(Deserialize, Validate, ToSchema)]
 pub struct CreateThoughtParams {
-    pub author_id: i32,
-
-    #[validate(length(min = 1, max = 128))]
+    #[validate(length(
+        min = 1,
+        max = 128,
+        message = "Content must be between 1 and 128 characters"
+    ))]
     pub content: String,
 }