feat(workspace): numbered lists and reliable markdown paste

- block type 'numbered' (/number): 1., a., i. by nesting, continues on
  Enter, an empty item ends the list; markdown export/import as 1.
- pasting: parser moved to lib/pasteOutline with tests; blank lines split
  paragraphs, numbered lists keep their type, indentation levels follow
  the widths in use (2, 3 or 4 spaces, tabs)
- text that stays in the focused block after pasting (a paragraph with
  line breaks) was dropped; the block now takes it

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/domain/models.go

@@ -441,6 +441,8 @@ func CompileBlocksToMarkdown(blocks []DocumentBlock) string {
 			sb.WriteString(indent + "- ```" + b.Lang + "\n" + b.Content + "\n" + indent + "  ```\n")
 		case "divider":
 			sb.WriteString(indent + "- ---\n")
+		case "numbered":
+			sb.WriteString(indent + "1. " + b.Content + "\n")
 		default:
 			sb.WriteString(indent + "- " + b.Content + "\n")
 		}