Add background definitions for SPC convective outlook risk products

internal/app/app_test.go

@@ -576,6 +576,10 @@ func TestGenerateReportIncludesSPCConvectivePromptStanzas(t *testing.T) {
 		"    spc_convective_discussion:",
 		"      included_because: categorical severity_rank >= 3",
 		"          label_text: Slight Risk",
+		"background_definition:",
+		"plain_language: Scattered severe storms possible.",
+		"official_description: Isolated intense storms are possible within the risk area, but severe weather is generally expected to be short-lived and/or not widespread.",
+		"relative_level: 2 of 5",
 		"          period_begins:",
 		"          period_ends:",
 		"          discussion: Severe thunderstorms may produce damaging winds during the afternoon.",