harness: a standing advisory is a defect

The %w advisory counted every fmt.Errorf without %w, including calls that create
an error rather than wrap one — so it fired permanently on correct code. It now
looks for a call that passes an err and drops the %w, which is the actual rule.

Recorded the general form in the loop's Verify step and in HARNESS.md: a warning
that fires on correct code and keeps firing is a defect in the check or the code,
resolved in that change. Two advisories have now been narrowed after firing on
code the harness itself mandates, and the count creeping from one to two was the
only signal either time.

verify.sh is at zero warnings, which is what makes the next one legible.

.claude/skills/khosra-feature-loop/SKILL.md

@@ -104,6 +104,10 @@ of real generated markup, or benchmark numbers.
 
 Budget failure: shrink the change, or stop and propose an ADR raising it. Never raise it silently.
 
+**A standing advisory is a defect.** If a warning fires on correct code and will keep firing, either the
+check is wrong or the code is — resolve which, in that change. Tolerated warnings are how the whole
+channel stops being read, and the count creeping from one to two is the only signal you get.
+
 Never write "should work", "this will now…", or your own diff summarised as a result. If you could
 not run something, say which and why.