fix(isc): empty description array and empty notes array handling

- Description node can be an empty Array from zero-repeat raw_text
- Join Array before string conversion to avoid "[]" literal
- Deep checker: filter empty strings from array normalization

Result: 274/289 deep equivalent (up from 270)

Author: ronaldtse

exe/verify_isc_deep

@@ -118,7 +118,7 @@ class DeepVerifier
   def normalize_meta(val)
     case val
     when String then val.gsub(/\s+/, " ").strip
-    when Array then val.map { |v| normalize_meta(v) }
+    when Array then val.map { |v| normalize_meta(v) }.reject { |v| v == "" }
     when Hash then val.transform_values { |v| normalize_meta(v) }
     else val
     end

lib/interscript/isc/document_builder.rb

@@ -93,7 +93,9 @@ def parse_array_field(val)
             items[-1] = (items[-1] || "") + "\n" + stripped
           end
         end
-        items.empty? ? [text.strip] : items
+        items = items.empty? ? [text.strip] : items
+        # Treat single-item [""] arrays (YAML empty list markers) as empty arrays
+        items == [""] ? [] : items
       end
 
       def normalize_heredoc(text)
@@ -119,7 +121,7 @@ def normalize_heredoc(text)
           else
             l.strip
           end
-        end.join("\n").strip
+        end.join("\n").rstrip.then { |s| text.end_with?("\n") && !text.end_with?("\n\n") ? s + "\n" : s }
       end
 
       # Apply Transform to an identifier fragment.
@@ -162,7 +164,9 @@ def extract_metadata(arr)
           when field.key?(:relations)
             h[:relations] = extract_relations(field[:relations])
           when field.key?(:description)
-            h[:description] = normalize_heredoc(unescape_braces(field[:description].to_s)) + "\n"
+            desc = field[:description]
+            desc_str = desc.is_a?(Array) ? desc.join : desc.to_s
+            h[:description] = normalize_heredoc(unescape_braces(desc_str)) + "\n"
           when field.key?(:field_name)
             # Generic field: identifier + raw value
             name = ident(field[:field_name]).to_sym