[Users] Add Get User by ID Route (GET /users/{userId})

[nourshoreibah]

User Story

As a user I want to retrieve a specific user by ID from the Users table.

Description

• Add the GET /users/{userId} route to the users Lambda using:
  node tools/lambda-cli.js add-route users GET /users/{userId}
• Implement lookup logic using Kysely (db.selectFrom('users').selectAll().where('userID', '=', userId)).
• Test using Swagger and Jest.

Acceptance Criteria

• Route returns user data for valid IDs.
• Swagger returns 404 for non-existent IDs.
• Jest tests cover valid, invalid, and missing parameters.