fix(cli): search limit counts visible results, filter before cap

Pass 0 (unlimited) to m.Search so the mail layer returns all matching
headers; the existing post-filter loop already caps at the caller's
limit, mirroring ListCmd. Add TestSearchLimitCountsVisibleOnly to prove
filtering happens before the cap.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/cli/agent.go

@@ -187,7 +187,7 @@ func SearchCmd(d Deps, account, folder string, sc mail.SearchCriteria, limit int
 		return d.emit(*fail)
 	}
 	defer done()
-	headers, err := m.Search(folder, sc, limit)
+	headers, err := m.Search(folder, sc, 0)
 	if err != nil {
 		return d.emit(Failure(CodeNetwork, err.Error()))
 	}