Add automated visual regression testing with Detox

[Smartdevs17]

Description

No visual regression testing exists. Implement screenshot-based testing with Detox for UI consistency.

Acceptance Criteria

• Detox configuration for iOS and Android
• Screenshot tests for all major screens
• Visual diff comparison in CI
• Baseline screenshot management
• Flaky test handling
• CI integration with artifact storage

Technical Scope

• e2e/
• .detoxrc.js
• .github/workflows/e2e-detox.yml
• Edge: device-specific rendering differences, test timing, baseline update workflow