Add iOS native support with a minimal Tauri 2 wrapper

Goal

Ship an iOS app using Tauri 2 with minimal changes to the current web app. Reuse the shared wrapper/build work from #3. Keep Svelte, HTML audio, browser Media Session, OPFS, and the Subsonic client initially; validate WKWebView independently rather than assuming Android or Safari/PWA behavior applies.

Scope

• Add the iOS Tauri target, app identity/icons, signing/provisioning, and build configuration.
• Document macOS/Xcode/Rust requirements, device builds, and TestFlight/App Store distribution requirements; keep signing secrets out of the repository.
• Reuse a native Vite build with bundled assets and PWA generation, registration, and update UI disabled.
• Preserve the existing web build/deployment workflow.
• Select a minimum iOS version and verify HTML audio, Media Session, OPFS reads/streamed writes, Navigation API, URLPattern, and other required APIs in WKWebView. Add only necessary compatibility fixes.
• Test authentication, browsing, artwork, streaming, and downloads against HTTPS servers, including CORS for the actual wrapper origin and App Transport Security behavior.
• Verify safe-area insets, keyboard resizing, and back/swipe navigation.
• Keep the packaged origin stable across updates and document that Safari/PWA data does not transfer automatically.

Background playback investigation

• Test the existing HTML audio/Media Session implementation on a real iPhone.
• Determine whether native audio-session configuration and the background-audio capability are needed for HTML audio playback.
• Verify automatic queue advancement with the screen locked and the UI backgrounded; background-audio configuration alone does not guarantee JavaScript execution.
• Introduce native playback or storage only if testing demonstrates a concrete limitation; document the findings before expanding scope.

Real-device acceptance tests

• Foreground streaming and seeking work.
• Lock-screen/Control Center metadata and controls, Bluetooth controls, interruptions, and audio-route changes behave correctly.
• Extended screen-off/background playback continues and advances automatically between tracks.
• Downloads survive restart and play after an airplane-mode cold launch.
• Verify large downloads, quotas/storage pressure, and behavior when backgrounding a download.
• App updates preserve credentials, queue, position, and downloaded music.
• Record lifecycle/process-recreation limitations and any differences from Android.

First milestone

An installable development build on an iPhone using the existing web player and storage. Background playback remains an acceptance-test question, not an assumed benefit of the wrapper. Native releases use the iOS distribution workflow, not the PWA updater.

Start by reviewing the shared wrapper/build work from #3 and the existing web player and storage behavior, then create the first installable iPhone development build with the native Vite and bundled-asset path. Validate the listed WKWebView APIs and foreground streaming, seeking, authentication, browsing, artwork, and downloads on a real device; the first milestone is an installable build, with background playback findings documented rather than assumed.