Feature/82/invalidate-jwt

[AmirAgassi]

🔒 Invalidate JWT #82

🔍 What's Included

• Added token_salt column to users table in migrations.
• Edited JWT generation and verification to use token_salt.
• Edited middleware and server logic to fetch and verify tokens with token_salt.

📁 Files Affected:

• backend/.sqlc/migrations/20241219000000_add_token_salt_to_users.sql
• backend/.sqlc/queries/users.sql
• backend/internal/jwt/*
• backend/internal/middleware/jwt.go
• backend/internal/server/*