Fix macOS Moonshine runtime bundling

[maxschmieder05-create]

Summary

Fixes the remaining macOS runtime failure after the Intel DMG fix: the app now runs locally on macOS, loads Moonshine, and packages the required shared libraries into the .app bundle.

Root cause

macOS was using the static sherpa-onnx build. On an Apple Silicon Mac, startup warm-up crashed during ONNX Runtime session creation with an uncaught Ort::Exception while loading the Moonshine model. Switching macOS to sherpa-onnx shared matches the other platforms and avoids the C++ exception crossing the Rust/static-library boundary.

There was also a local build issue: Tauri validates bundle.resources paths before beforeBundleCommand can stage runtime libraries, so local macOS cargo check / tauri dev needs validation stubs just like CI.

Changes

• Switch macOS sherpa-onnx from static to shared.
• Create bundle resource validation stubs from build.rs for local builds.
• Stage macOS .dylib runtime libraries in stage-bundle-resources.cjs.
• Bundle the macOS dylibs into Contents/MacOS.
• Add @executable_path rpath before bundling so dyld can find the staged dylibs.
• Make the staging script handle debug builds where Tauri sets a target triple but Cargo outputs to target/debug.
• Update build docs/changelog for shared runtime library staging.

Validation

• node --check scripts/stage-bundle-resources.cjs
• cargo fmt --check
• cargo check --all-targets
• npm run tauri -- build --debug --bundles app
• Launched the debug .app bundle directly with VIBE_TO_TEXT_SELF_TEST=1; Moonshine loaded and self-test passed 3/3 WAV fixtures.

Note: Tauri still emits an unrelated warning that the bundle identifier dev.vibetotext.app ends with .app.