Implement QR scanner

[2witstudios]

Epic 5: iOS App — Models & Networking — Issue 6/6

Source: 3-agent worktree — production-grade AVCaptureSession implementation

Description

Camera-based QR code scanner for pairing with ppg server.

Acceptance Criteria

• UIViewRepresentable wrapping AVCaptureSession
• QR code detection via AVCaptureMetadataOutput
• Parse ppg://connect?host=...&port=...&ca=...&token=... scheme
• Double-scan prevention (process each QR code only once)
• Error alerts for invalid QR codes
• Video preview layer with proper bounds management
• Camera permission request handling
• Proper session lifecycle (start/stop on appear/disappear)

Files to Create

• ios/PPGMobile/PPGMobile/Views/Settings/QRScannerView.swift (new)