feat: implement QR scanner

[2witstudios]

Summary

• Implements camera-based QR code scanner for pairing with ppg server
• Parses ppg://connect?host=...&port=...&ca=...&token=... URL scheme
• Adds ca (certificate authority) field to ServerConnection for TLS pinning

Changes

QRScannerView.swift (new)

• QRScannerView — SwiftUI view with camera permission handling, error alerts, scan overlay
• QRCameraView — UIViewRepresentable wrapping AVCaptureSession with AVCaptureMetadataOutput for QR detection
• CameraPreviewView — UIView subclass with layoutSubviews for proper preview bounds
• Double-scan prevention via hasScanned flag in coordinator
• Session lifecycle: starts on creation, stops via dismantleUIView

ServerConnection.swift (updated)

• New ca: String? field for TLS certificate pinning
• Updated fromQRCode() to parse ppg://connect?... query-param format
• baseURL/wsURL auto-select https/wss when ca is present

Test plan

• Verify camera permission prompt appears on first launch
• Verify denied permission shows "Open Settings" fallback UI
• Scan valid ppg://connect?host=...&port=...&token=... QR — should connect
• Scan valid QR with &ca=... — should connect over TLS
• Scan non-ppg QR code — should show error alert
• Scan invalid ppg QR (missing token) — should show error alert
• Verify double-scan prevention (same QR not processed twice)
• Verify camera preview resizes correctly on rotation

Closes #81

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📥 Commits

Reviewing files that changed from the base of the PR and between 34deb69 and 81129df.

📒 Files selected for processing (4)

• ios/PPGMobile/PPGMobile/Models/ServerConnection.swift
• ios/PPGMobile/PPGMobile/Models/ServerConnectionTests.swift
• ios/PPGMobile/PPGMobile/Views/Settings/QRScannerView.swift
• src/commands/spawn.test.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch ppg/issue-81-qr-scanner

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