Add a native iOS client for relay-based file sharing

The SwiftUI app bundles the Go swarm engine through gomobile, so an iPhone is a real peer using the existing PAKE handshake, chunk verification, and relay fallback. XcodeGen builds the project and devicectl installs it on the paired phone.

apps/ios/build-go.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+# Build the Go swarm engine as an iOS XCFramework. Run this before
+# `xcodegen generate` whenever the Go bridge or anything under src/ changes.
+set -euo pipefail
+
+HERE="$(cd "$(dirname "$0")" && pwd)"
+TOOLS="$HERE/.build/tools"
+mkdir -p "$TOOLS"
+
+cd "$HERE/GoBridge"
+
+# Install the exact gomobile/gobind versions recorded in this module. The
+# tools live in the app folder so they are easy to delete and never leak
+# into the rest of the repo.
+GOBIN="$TOOLS" go install golang.org/x/mobile/cmd/gomobile golang.org/x/mobile/cmd/gobind
+export PATH="$TOOLS:$PATH"
+
+gomobile init
+rm -rf "$HERE/Share.xcframework"
+gomobile bind -target=ios -o "$HERE/Share.xcframework" .
+
+echo "Built $HERE/Share.xcframework"