fix(go-skill): Elasticsearch skill search field mapping (#16611)

## Summary

Fix Elasticsearch-backed skill search by mapping skill search fields to
their indexed token fields.

`name`, `tags`, `description`, and `content` are stored for display but
are not searchable in the skill ES mapping. Search queries now target
`name_tks`, `tags_tks`, `description_tks`, and `content_tks`.

## Testing

- Ran Go unit tests:

```bash
/usr/local/go/bin/go test -count=1 ./internal/engine/elasticsearch
```

- Frontend verification:
    1. Open /files/skills.
    2. Enter a skill space.
3. Reindex the skill space if existing skills were created before this
fix.
    4. Search by skill name or description keyword.
    5. Confirm matching skills are returned.

internal/engine/elasticsearch/chunk.go

@@ -1746,6 +1746,9 @@ func buildQueryStringQuery(matchText *types.MatchTextExpr, vectorSimilarityWeigh
 			fields = []string{"title_tks^10", "title_sm_tks^5", "important_kwd^30", "important_tks^20", "question_tks^20", "content_ltks^2", "content_sm_ltks"}
 		}
 	}
+	if isSkillIndex {
+		fields = mapSkillSearchFields(fields)
+	}
 	if isMemoryIndex {
 		fields = mapMemoryMessageESFields(fields, true)
 	}
@@ -1768,6 +1771,29 @@ func buildQueryStringQuery(matchText *types.MatchTextExpr, vectorSimilarityWeigh
 	}
 }
 
+func mapSkillSearchFields(fields []string) []string {
+	mapped := make([]string, 0, len(fields))
+	for _, field := range fields {
+		name, boost, hasBoost := strings.Cut(field, "^")
+		switch name {
+		case "name":
+			name = "name_tks"
+		case "tags":
+			name = "tags_tks"
+		case "description":
+			name = "description_tks"
+		case "content":
+			name = "content_tks"
+		}
+		if hasBoost {
+			mapped = append(mapped, name+"^"+boost)
+		} else {
+			mapped = append(mapped, name)
+		}
+	}
+	return mapped
+}
+
 // buildRankFeatureQuery builds rank_feature queries for learning to rank
 func buildRankFeatureQuery(rankFeature map[string]float64) []map[string]interface{} {
 	if rankFeature == nil || len(rankFeature) == 0 {

internal/engine/elasticsearch/chunk_helpers_test.go

@@ -4,8 +4,37 @@ import (
 	"reflect"
 	"strings"
 	"testing"
+
+	"ragflow/internal/engine/types"
 )
 
+func TestBuildQueryStringQueryMapsSkillFieldsToTokenFields(t *testing.T) {
+	query := buildQueryStringQuery(&types.MatchTextExpr{
+		MatchingText: "test",
+		Fields:       []string{"name^10", "tags^5", "description^3", "content^1"},
+	}, 0, true, false)
+
+	queryString, ok := query["query_string"].(map[string]interface{})
+	if !ok {
+		t.Fatalf("query_string missing from %#v", query)
+	}
+	assertEqual(t, queryString["fields"], []string{"name_tks^10", "tags_tks^5", "description_tks^3", "content_tks^1"})
+	assertEqual(t, queryString["query"], "test")
+}
+
+func TestBuildQueryStringQueryKeepsDocumentFieldsUnchanged(t *testing.T) {
+	query := buildQueryStringQuery(&types.MatchTextExpr{
+		MatchingText: "test",
+		Fields:       []string{"name^10"},
+	}, 0, false, false)
+
+	queryString, ok := query["query_string"].(map[string]interface{})
+	if !ok {
+		t.Fatalf("query_string missing from %#v", query)
+	}
+	assertEqual(t, queryString["fields"], []string{"name^10"})
+}
+
 func TestElasticsearchGetFieldsFiltersAndUsesIDFallback(t *testing.T) {
 	engine := &elasticsearchEngine{}
 	chunks := []map[string]interface{}{