[codex] fix macOS app translation flow

[MarsDoge]

Summary

Fixes the macOS menu-bar app translation flow after installing the app to /Applications/LLMTranslateMac.app.

• Sets explicit status-menu item targets so menu actions do not depend on responder-chain dispatch.
• Adds Test Translation and Show Diagnostics menu items for separating provider/CLI issues from selected-text permission issues.
• Installs the app to a stable /Applications/LLMTranslateMac.app path via build-app.sh --install.
• Signs the generated app bundle with a stable bundle identifier for macOS Accessibility permissions.
• Bundles the existing bin/ and lib/ CLI resources inside the app so /Applications/LLMTranslateMac.app is self-contained.
• Defaults the app to mymemory whenever LLM_TRANSLATE_PROVIDER is not explicitly configured.
• Improves error reporting, writes diagnostics to ~/Library/Logs/LLMTranslateMac.log, and fixes result panel text visibility.

Why

The app could launch while translation failed or appeared blank because the installed /Applications app could not reliably find the repository CLI, menu dispatch was ambiguous, and errors were surfaced as generic Swift enum messages. Accessibility permission also needs a stable app path and bundle identity.

Validation

• swift build in macos/LLMTranslateMac
• ./scripts/build-app.sh --install in macos/LLMTranslateMac
• bash -n macos/LLMTranslateMac/scripts/build-app.sh
• shellcheck macos/LLMTranslateMac/scripts/build-app.sh
• Bundle CLI smoke test: printf 'Hello, world!' | /Applications/LLMTranslateMac.app/Contents/Resources/llm-translate/bin/llm-translate -p mymemory -t zh-CN
• Local app log confirmed Test Translation succeeded: 您好，世界！