Set up a dedicated Staging environment mapped to the develop branch

[AlAfiz]

Description

We need a persistent environment that exactly mirrors production but runs on the Stellar Testnet, allowing for final integration testing before a mainnet release.

Acceptance Criteria

• Establish a Git workflow where feature branches merge into develop, and develop merges into main for releases.
• Configure Vercel (or target hosting) to auto-deploy the develop branch to a static URL (e.g., staging.tradeflow.app).
• Ensure the staging environment has distinct environment variables (Testnet API keys, Testnet Soroban Contract IDs).
• Protect the staging environment with basic HTTP Auth or restrict access if it contains proprietary pre-release features.

Technical Details

• Ensure database connections for staging point to an isolated staging DB, never production.