* feat(darwin): add interactive terminal password prompt for keychain unlock (#556)
* test: add unit tests for keyretriever and address review feedback
- Add errStorageNotFound sentinel error for precise error matching
- Non-TTY TerminalPasswordRetriever returns nil silently (review #558)
- Add darwin tests: findStorageKey, empty password, non-TTY skip
- Add linux tests: FallbackRetriever peanuts key, DefaultRetriever chain
* fix: add nolint:unused for errStorageNotFound on Windows, clean up error message
errStorageNotFound is only used on darwin/linux; Windows lint flagged it
as unused. Also simplify error format to avoid "storage" duplication.
* fix: add nolint:unused for errStorageNotFound, simplify error message
errStorageNotFound is only referenced on darwin and linux; Windows lint
flags it as unused. Also remove redundant "storage" prefix from the
error format string.