Support iOS 15 devices

[vnby]

Summary

• lower the iOS deployment target from 16.0 to 15.0
• pin FlyingFox to 0.16.0 / swift-syntax 509.0.0 so dependencies still build for iOS 15
• adapt the portal server startup call for FlyingFox 0.16.0
• guard XCUIDevice.hasHardwareButton behind iOS 16 availability and remove iOS 17/18-only hardware buttons from the iOS 15-safe enum
• clean the scheme/test plan to remove stale/duplicated test targets that make physical-device test planning brittle
• remove the hard-coded development team from project settings so contributors can use their own signing team

Why

Older but still usable devices such as iPhone 7 are capped at iOS 15.8.x. The current project requires iOS 16+ and pulls newer dependencies/APIs, so these devices cannot run the portal even though the required XCTest/UIAutomation primitives are available on iOS 15.

Validation

• Built the clean PR branch for generic physical iOS using Xcode 26.2 with signing disabled:

DEVELOPER_DIR=/Applications/Xcode_26.2.app/Contents/Developer \
  xcodebuild build-for-testing \
  -project droidrun-ios-portal.xcodeproj \
  -scheme droidrun-ios-portal \
  -destination "generic/platform=iOS" \
  -derivedDataPath /tmp/ios-portal-pr-clean-derived \
  CODE_SIGNING_ALLOWED=NO \
  -skipPackagePluginValidation \
  -skipMacroValidation

Result: ** TEST BUILD SUCCEEDED **

• Also tested an equivalent signed local build on an iPhone 7 (iPhone9,3) running iOS 15.8.7:
  • Xcode 26.2 was required; Xcode 26.5 appears to have a test-planning regression on this old device.
  • After trusting the developer profile and enabling UI Automation on device, the portal server started on port 6643.
  • Verified /device/date, /state, screenshot capture, and hardware home key control through a usbmux forward.