runtime(zip): fix failure on Windows CI

runtime(zip): fix failure on Windows CI

Problem:  The zip autoload script aborts loading when the "zip"
          command is not available, so even read-only browsing of an
          archive fails with E117 (zip#Browse undefined) on systems
          that have "unzip" but not "zip" (e.g. the Windows CI
          runner).  Regressed in b0e0b22.
Solution: Drop the load-time executable gate and check each command
          per operation instead, so a missing "zip" only affects
          writing.  Update the test to match the reworded message.

Signed-off-by: Christian Brabandt <cb@256bit.org>