fix(outages): format numeric portal dates as integers

Portal date fields arrive as numbers; fmt's %v rendered them in scientific
notation, so the "current outage" filter could not parse them and kept past
outages (a 'Прошлые' record leaked through). Format integer-valued attributes
explicitly.

internal/adapters/arcgis/client.go

@@ -191,14 +191,22 @@ func codeKey(v any) string {
 	}
 }
 
+// stringOf renders an attribute value as a string. The important case is
+// numeric dates: fmt's %v turns a float64 into scientific notation ("1.79e+12")
+// which the date parser cannot read, so integers are formatted explicitly.
 func stringOf(v any) string {
-	if s, ok := v.(string); ok {
-		return s
-	}
-	if v == nil {
+	switch t := v.(type) {
+	case nil:
 		return ""
+	case string:
+		return t
+	case float64:
+		return strconv.FormatInt(int64(t), 10)
+	case json.Number:
+		return t.String()
+	default:
+		return fmt.Sprintf("%v", v)
 	}
-	return fmt.Sprintf("%v", v)
 }
 
 // actionFor maps a portal system name to the canonical action code used by the