fix(brand-questions): accept generic search terms in lexicon validation

Search terms like "全屋定制" or "GEO排名优化" were rejected as invalid because
both the Vue candidate validator and the Go question_metadata classifier
required interrogative cues (什么/如何/为什么/...). Lexicon entries are search
terms, not questions, so require only letters or digits plus the existing
4-char minimum. Rename helpers to searchTermLooksValid/questionLooksValid
to reflect the looser semantics, and relabel the navigation entry from
"公司和词库" to "品牌和词库" to match the actual domain.

server/internal/tenant/app/question_metadata_classify.go

@@ -123,17 +123,14 @@ func questionLooksValid(text string) bool {
 	if utf8.RuneCountInString(trimmed) < 4 {
 		return false
 	}
-	hasLetterOrNumber := false
+	hasSearchTermChar := false
 	for _, r := range trimmed {
 		if unicode.IsLetter(r) || unicode.IsNumber(r) {
-			hasLetterOrNumber = true
+			hasSearchTermChar = true
 			break
 		}
 	}
-	if !hasLetterOrNumber {
-		return false
-	}
-	return containsAny(strings.ToLower(trimmed), []string{"?", "？", "什么", "如何", "怎么", "哪", "为什么", "是否", "能不能", "适合", "区别", "对比", "推荐"})
+	return hasSearchTermChar
 }
 
 func containsAny(value string, needles []string) bool {