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>

frontend/src/lib/__tests__/outlineList.test.ts

@@ -0,0 +1,27 @@
+import { describe, it, expect } from 'vitest';
+import { listLabel, numberedLabels } from '../outlineList';
+import type { DocumentBlock } from '../types';
+
+const blk = (id: string, level: number, type: DocumentBlock['type'] = 'numbered'): DocumentBlock => ({
+  id, documentId: 'd', type, content: id, level, position: 0,
+});
+
+describe('numbered lists', () => {
+  it('formats numbers, letters and roman numerals by depth', () => {
+    expect(listLabel(3, 0)).toBe('3.');
+    expect(listLabel(2, 1)).toBe('b.');
+    expect(listLabel(27, 1)).toBe('aa.');
+    expect(listLabel(4, 2)).toBe('iv.');
+    expect(listLabel(1, 3)).toBe('1.');
+  });
+
+  it('counts siblings, nests and restarts after other blocks', () => {
+    const labels = numberedLabels([
+      blk('a', 0), blk('a1', 1), blk('a2', 1), blk('a2i', 2), blk('b', 0),
+      blk('note', 0, 'text'), blk('c', 0), blk('plain', 1, 'text'), blk('c1', 2),
+    ]);
+    expect(Object.fromEntries(labels)).toEqual({
+      a: '1.', a1: 'a.', a2: 'b.', a2i: 'i.', b: '2.', c: '1.', c1: 'a.',
+    });
+  });
+});