fix: fallback on invalid ai table output

internal/ai/service_test.go

@@ -0,0 +1,29 @@
+package ai
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestFallbackTableAnalysisUnparsedProfile(t *testing.T) {
+	result := fallbackTableAnalysis(TableAnalysisInput{
+		Topic:    "销售分析",
+		FileID:   "file1",
+		FileName: "sales.xlsx",
+		FileType: "xlsx",
+		FileSize: 5149,
+		Profile:  TableProfile{Parsed: false, Message: "source file is not available locally"},
+	}, Usage{Model: "deepseek-flash"}, "AI 输出格式异常，已使用兜底解读。")
+	if result.Title != "销售分析" {
+		t.Fatalf("Title=%q, want 销售分析", result.Title)
+	}
+	if strings.TrimSpace(result.Interpretation) == "" {
+		t.Fatal("Interpretation is empty")
+	}
+	if len(result.Alerts) < 2 {
+		t.Fatalf("Alerts len=%d, want at least 2", len(result.Alerts))
+	}
+	if got := result.Metrics[len(result.Metrics)-1].Value; got != "未解析" {
+		t.Fatalf("last metric value=%q, want 未解析", got)
+	}
+}