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/Cargo.lock

@@ -2408,6 +2408,7 @@ dependencies = [
  "serde",
  "serde_json",
  "utoipa",
+ "uuid",
  "validator",
 ]
 
@@ -4894,6 +4895,7 @@ dependencies = [
  "quote",
  "regex",
  "syn 2.0.104",
+ "uuid",
 ]
 
 [[package]]