feat: Refactor user and thought models to use UUIDs instead of integers

- Updated user and thought models to utilize UUIDs for primary keys.
- Modified persistence functions to accommodate UUIDs for user and thought IDs.
- Implemented tag functionality with new Tag and ThoughtTag models.
- Added migration scripts to create new tables for tags and thought-tag relationships.
- Enhanced thought creation to parse hashtags and link them to thoughts.
- Updated tests to reflect changes in user and thought ID types.

thoughts-backend/migration/src/m20250906_100000_add_profile_fields.rs

@@ -36,8 +36,8 @@ impl MigrationTrait for Migration {
                 Table::create()
                     .table(TopFriends::Table)
                     .if_not_exists()
-                    .col(integer(TopFriends::UserId).not_null())
-                    .col(integer(TopFriends::FriendId).not_null())
+                    .col(uuid(TopFriends::UserId).not_null())
+                    .col(uuid(TopFriends::FriendId).not_null())
                     .col(small_integer(TopFriends::Position).not_null())
                     .primary_key(
                         Index::create()