- Add backend param to isCLIProxyInstalled(), getCLIProxyPath(),
getInstalledCliproxyVersion(), installCliproxyVersion()
- Update getBinaryStatus() to pass backend to all helper functions
- Add getBackendLabel() helper for dynamic CLI messages
- Replace hardcoded "CLIProxy Plus" strings with dynamic labels
- Pass --backend flag through install/update command handlers
- Import CLIProxyBackend type from types.ts instead of redefining
Setting `cliproxy.backend: original` in config.yaml now correctly
uses the original backend for version pins and binary operations.