Remove sensitive .env files and add .env.example templates

[AnaJotta]

🔒 Problem

The repository contains .env files (gateway.env, itest.env, userservice.env) with sensitive information such as OAuth secrets, Redis passwords, and database credentials.

🧩 Solution

• Removed .env files from version control.
• Added .env.example templates for each service.
• Updated .gitignore to prevent committing real environment files.

⚠️ Note

The previous secrets still exist in the Git history.
It is recommended to use a tool like bfg-repo-cleaner to remove them permanently.