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/models/Cargo.toml

@@ -17,6 +17,7 @@ sea-orm = { workspace = true, features = [
   "runtime-tokio-rustls",
   "macros",
 ] }
+uuid = { version = "1.18.1", features = ["v4", "serde"] }
 validator = { workspace = true, features = ["derive"] }
 utoipa = { workspace = true }