Bring the verify sheet closer to Android

Summary

Restructures the iOS verification sheet after bitchat-android's VerificationSheet, using iOS controls in place of Material ones.

• Tabs. A segmented "my QR" / "scan" control under the header replaces the bottom "scan someone else's qr" toggle. Settings and Notices already use the same control. A successful scan returns to my QR, as on Android.
• My QR. The code sits on a white card with a quiet zone, white in every theme so it scans reliably. The nickname and a muted "bitchat" line are under it. The raw bitchat://verify URL is no longer printed under the code, as on Android. Long-pressing (right-clicking on macOS) the card copies it, which keeps the Mac app's paste box usable for Macs without a camera; the old sheet allowed this through selectable URL text.
• Scan. The camera preview fills the available space, with a reticle and a caption pill on dark material.
• Camera access denied. The scanner explains that camera access is needed and offers open settings, because iOS can't re-prompt once access is denied. iOS no longer says "paste a QR below"; that field only exists on macOS.
• Remove verification. A full-width bordered button with the destructive role. It uses system red: the matrix alertRed was too dark to read on black.
• Typography. Text goes through bitchatFont, so it follows Dynamic Type. My QR scrolls at large sizes.

Screenshots

Rendered in the iPhone 17 simulator with mock identity keys.

The simulator has no camera, so the scan tab shows the reticle and caption over an empty preview.

Other changes

• SystemSettings.camera opens the camera privacy pane on macOS and the app's Settings page on iOS.
• 5 new strings in all 30 locales: verification.tab.my_qr, verification.tab.scan, verification.tab.picker_label, verification.scan.camera_permission and verification.scan.no_camera. open settings reuses location_channels.action.open_settings, and remove verification reuses fingerprint.action.remove_verification. The translations are new and could use a native-speaker check.
• The old "show my qr", "scan someone else's qr" and "remove verification" labels were literals missing from the string catalog. They're gone.

Testing

• swift test passes: 2198 tests, including ViewSmokeTests and the localization checks.
• The iOS simulator build succeeds with no new warnings. The macOS build succeeds through SwiftPM.
• Rendered both themes in light and dark, the verified-peer state and the scan tab in the simulator (above).
• Not yet checked:
  • the live camera on a device
  • the camera-denied state and its Settings link
  • long-press copy
  • the largest Dynamic Type sizes
  • the macOS sheet on screen

🤖 Generated with Claude Code