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/pasteOutline.ts

@@ -0,0 +1,109 @@
+import type { BlockType } from './types';
+
+// Turns pasted (Markdown) text into outline items: headings, todos, bullets, numbered items, dividers,
+// fenced code and paragraphs. A blank line ends a paragraph; indentation becomes the nesting level.
+
+export interface PastedItem {
+  type: BlockType;
+  checked?: boolean;
+  content: string;
+  indent: number;
+}
+
+function leadingWidth(line: string): { width: number; rest: string } {
+  let width = 0;
+  let i = 0;
+  while (i < line.length && (line[i] === ' ' || line[i] === '\t')) {
+    width += line[i] === '\t' ? 4 : 1;
+    i++;
+  }
+  return { width, rest: line.slice(i) };
+}
+
+export function parsePastedLines(rawLines: string[]): PastedItem[] {
+  // Indentation steps differ (2, 3 or 4 spaces, tabs): the distinct widths in use are the levels
+  const widths = Array.from(
+    new Set(rawLines.filter((l) => l.trim() !== '').map((l) => leadingWidth(l).width))
+  ).sort((a, b) => a - b);
+  const levelOf = (w: number) => Math.max(0, widths.indexOf(w));
+
+  const items: PastedItem[] = [];
+  let current: PastedItem | null = null;
+  let inCode = false;
+  let afterHeading = false;
+
+  const flush = () => {
+    if (current) {
+      current.content = current.content.trimEnd();
+      items.push(current);
+      current = null;
+    }
+  };
+
+  for (const rawLine of rawLines) {
+    if (inCode) {
+      if (current) (current as PastedItem).content += '\n' + rawLine;
+      if (rawLine.trim().startsWith('```')) {
+        inCode = false;
+        flush();
+      }
+      continue;
+    }
+    if (rawLine.trim().startsWith('```')) {
+      inCode = true;
+      flush();
+      current = { type: 'text', content: rawLine, indent: 0 };
+      afterHeading = false;
+      continue;
+    }
+
+    const { width, rest } = leadingWidth(rawLine);
+    const indent = levelOf(width);
+    const line = rest.trimEnd();
+
+    // A blank line ends the paragraph or list item
+    if (line === '') {
+      flush();
+      continue;
+    }
+
+    const heading = line.match(/^(#{1,3})\s+(.*)$/);
+    if (heading) {
+      flush();
+      afterHeading = true;
+      items.push({ type: (['h1', 'h2', 'h3'] as const)[heading[1].length - 1], content: heading[2], indent });
+      continue;
+    }
+    if (/^(?:-{3,}|\*{3,}|_{3,})$/.test(line)) {
+      flush();
+      afterHeading = false;
+      items.push({ type: 'divider', content: '---', indent });
+      continue;
+    }
+
+    const todo = line.match(/^[-*+]\s*\[([ xX])\]\s*(.*)$/);
+    const bullet = line.match(/^[-*+•]\s+(.*)$/);
+    const numbered = line.match(/^\d+[.)]\s+(.*)$/);
+    if (todo || bullet || numbered) {
+      flush();
+      afterHeading = false;
+      current = todo
+        ? { type: 'todo', checked: todo[1].toLowerCase() === 'x', content: todo[2], indent }
+        : numbered
+        ? { type: 'numbered', content: numbered[1], indent }
+        : { type: 'text', content: bullet![1], indent };
+      continue;
+    }
+
+    // Plain text: continues the paragraph or list item above (a wrapped line), else starts a paragraph
+    if (current && !afterHeading) {
+      (current as PastedItem).content += '\n' + line;
+    } else {
+      flush();
+      current = { type: 'text', content: line, indent };
+    }
+    afterHeading = false;
+  }
+  flush();
+  return items;
+}