feat(knowledge): multi-query retrieval with LLM query rewrite

Add a shared structured query builder (knowledge_query.go) and switch
all generation paths to it, so retrieval queries carry task intent
(type, brand, region, keywords, key points) instead of a raw prompt.

ResolveContext now rewrites the query into multiple sub-questions via
the URL-markdown model, embeds and searches each, and merges/dedupes
candidates before rerank; falls back to parsed fallback questions when
rewrite is unavailable or returns too few. Resolve logs gain query
list, count, and rewrite stage/model for observability.

- knowledge_query.go/_test.go: BuildKnowledgeQuery + intent normalization
- knowledge_service.go: per-query embed/search loop, query rewrite, logs
- template_prompt/template_service/prompt_generate/article_imitation/
  kol_generation_worker: adopt the shared query builder
- generation_observability: richer task error logging

server/internal/tenant/app/generation_observability_test.go

@@ -4,6 +4,7 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/geo-platform/tenant-api/internal/shared/response"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -91,6 +92,34 @@ func TestGenerationTaskMetricsRecordsEventsAndPrometheus(t *testing.T) {
 	assert.True(t, strings.HasSuffix(lastEventLine, " 1"), lastEventLine)
 }
 
+func TestFormatGenerationFailureKeepsAppErrorBriefForUI(t *testing.T) {
+	err := response.ErrServiceUnavailable(50353, "embedding_failed", "request siliconflow: timeout")
+
+	got := formatGenerationFailure("knowledge_resolve", err)
+
+	assert.Equal(t, "知识库检索失败 [knowledge_resolve]: embedding_failed", got)
+}
+
+func TestGenerationTaskErrorFieldsIncludesAppErrorDetailForLogs(t *testing.T) {
+	err := response.ErrServiceUnavailable(50353, "embedding_failed", "request siliconflow: timeout")
+
+	fields := GenerationTaskErrorFields(err)
+	values := map[string]any{}
+	for _, field := range fields {
+		switch {
+		case field.String != "":
+			values[field.Key] = field.String
+		case field.Integer != 0:
+			values[field.Key] = int(field.Integer)
+		}
+	}
+
+	assert.Equal(t, "embedding_failed", values["error_message"])
+	assert.Equal(t, "request siliconflow: timeout", values["error_detail"])
+	assert.Equal(t, 50353, values["error_code"])
+	assert.Equal(t, 503, values["http_status"])
+}
+
 func findPrometheusMetricLine(output, metricName string) string {
 	for _, line := range strings.Split(output, "\n") {
 		if strings.HasPrefix(line, metricName+"{") || strings.HasPrefix(line, metricName+" ") {