Return the authority that was validated, and test the hint's absence

Two follow-ups from the re-review.

parseEntireCloneURL validated the raw authority and then returned url.Parse's reading of it. The two agree for everything validateClusterHost accepts — a bare host[:port] parses to itself — so this changes nothing today, which a probe of fifteen hostile inputs confirms. It returns the validated value because that is the version that stays correct without anyone having to know the argument, and the last thing a spec refresh broke here was an assumption nobody restated.

The hint that stops naming an unusable command had no test. Both branches that print one are covered now, plus the case where a path exists and the hint is worth printing. Reverted against the old bare-name fallback, both fail with the entire repo view web they exist to prevent.