feat(ios): a sideloadable iOS client over the shared Rust engine

A SwiftUI app that drives the same UniFFI engine as Android: Rust owns the
Proton sessions, SQLite and every decrypted byte, and Swift asks it questions
off the main thread. Playback goes through MPVKit's libmpv, with the pstr://
stream protocol ported from the Android JNI half, and secrets live in the
Keychain.

scripts/build-ios.sh builds the static library for aarch64-apple-ios, writes
the Swift bindings (module PstrBridge), generates the Xcode project with
XcodeGen and packages an unsigned .ipa for SideStore or AltStore, which
re-sign it with the viewer's own Apple ID. The generated project, Info.plist
and build output are ignored.

crates/pstr-android/uniffi.toml

@@ -2,3 +2,9 @@
 # UniFFI's default JVM cleaner references java.lang.ref.Cleaner (API 33).
 # Android uses the JNA cleaner, which is available on our minSdk 31 runtime.
 disable_java_cleaner = true
+
+[bindings.swift]
+# The iOS client (`ios/`) compiles the generated file straight into the app
+# target and reaches the C side through its bridging header, so the names are
+# what that header and `ios/project.yml` expect.
+module_name = "PstrBridge"