fix(config): use macOS login item autostart

[StudentWeis]

Summary

Fixes macOS autostart by registering Ropy as a Login Item so it appears in System Settings, while removing the stale LaunchAgent entry that pointed at the .app directory.

Linked Issue

Closes #140

Changes

• Use auto-launch AppleScript Login Item mode on macOS instead of writing a LaunchAgent plist.
• Resolve bundled macOS builds to the .app path expected by Login Items.
• Clean up the legacy ~/Library/LaunchAgents/Ropy.plist entry during autostart sync.
• Add regression tests for bundle path resolution and sync decisions.

Testing

• scripts/precheck.sh passes locally
• New / updated tests cover the change

Self-Check

• PR title follows Conventional Commits
• No hardcoded user-facing strings — i18n keys added to all locale files
• Errors defined with thiserror (no manual impl Display/Error)
• No unrelated changes mixed in