fix(tauri): resolve oneshot in iOS open_external_url (unblocks iOS build)

[sonegillis1]

Problem

cargo tauri ios build (target aarch64-apple-ios) fails to compile src-tauri/src/lib.rs:

error[E0433]: failed to resolve: use of unresolved module or unlinked crate `oneshot`
    --> src/lib.rs:1398   let (tx, rx) = oneshot::channel();
error[E0282]: type annotations needed   (x2, downstream fallout)

The iOS-only branch of open_external_url uses oneshot::channel() but nothing brings oneshot into scope. This has been broken on main since the code was written — iOS isn't built in CI (only the macOS DMG is), so it never got caught.

Fix

tokio (with features = ["full"]) is already a dependency, so qualify it:

let (tx, rx) = tokio::sync::oneshot::channel();

tokio::sync::oneshot's Receiver::await returns Result<T, RecvError>, which the existing .unwrap_or_else(|_| Err(...)) already flattens correctly — no other changes needed.

Verification

cargo check --target aarch64-apple-ios --lib → Finished (0 errors). Local make tauri-ios-build then archives + uploads to App Store Connect successfully.

🤖 Generated with Claude Code