feat: Add macro support

New: macros.ts with MacroDef, parseBlockMacro, matchInlineMacro,
buildMacroTags, processInlineMacros.

Macro syntax:
  @user                     — bare, no args
  @user()                   — empty parens, same as bare
  @npc(Goblin King)         — self-closing with args
  @style(box center         — block: no closing paren on first line
  Content here.             — content on subsequent lines
  )                         — closing paren on its own line

Unknown macro names now render as an error:
  <span class="ribbit-error">Unknown macro: @bogus</span>

The verbatim keyword causes the contents to render as literals and also
preserves line breaks.

test/test_hopdown.js

@@ -407,6 +407,96 @@ try {
 }
 eq('invalid precedence throws', String(threw), 'true');
 
+// ── 24. Macros ──────────────────────────────────────────
+const macroConverter = new dom.window.ribbit.HopDown({
+    macros: [
+        {
+            name: 'user',
+            toHTML: () => '<a href="/user">TestUser</a>',
+            selector: 'A[href="/user"]',
+            toMarkdown: () => '@user',
+        },
+        {
+            name: 'npc',
+            toHTML: ({ keywords }) => {
+                const name = keywords.join(' ');
+                const target = name.replace(/ /g, '');
+                return '<a href="/NPC/' + target + '">' + name + '</a>';
+            },
+            selector: 'A[href^="/NPC/"]',
+            toMarkdown: (el) => '@npc(' + el.textContent + ')',
+        },
+        {
+            name: 'toc',
+            toHTML: ({ params }) =>
+                '<aside class="toc" data-depth="' + (params.depth || '3') + '"></aside>',
+        },
+        {
+            name: 'style',
+            toHTML: ({ keywords, content }) => {
+                const classes = keywords.join(' ');
+                return '<div class="' + classes + '">' + (content || '') + '</div>';
+            },
+            selector: 'DIV[class]',
+            toMarkdown: (el, convert) => {
+                return '\n\n@style(' + el.className + '\n' + convert.children(el) + '\n)\n\n';
+            },
+        },
+    ],
+});
+const MH = macroConverter.toHTML.bind(macroConverter);
+const MM = macroConverter.toMarkdown.bind(macroConverter);
+function mrt(md) { return MM(MH(md)); }
+
+// Self-closing macros
+eq('macro: bare name', MH('hello @user world'), '<p>hello <a href="/user">TestUser</a> world</p>');
+eq('macro: empty parens', MH('hello @user() world'), '<p>hello <a href="/user">TestUser</a> world</p>');
+eq('macro: with keywords', MH('@npc(Goblin King)'), '<p><a href="/NPC/GoblinKing">Goblin King</a></p>');
+has('macro: with params', MH('@toc(depth="2")'), 'data-depth="2"');
+
+// Unknown macro — error
+has('macro: unknown renders error', MH('@bogus'), 'ribbit-error');
+has('macro: unknown shows name', MH('@bogus'), '@bogus');
+
+// Email addresses not matched
+eq('macro: email not matched', MH('user@example.com'), '<p>user@example.com</p>');
+
+// Block macros
+has('macro: block content processed', MH('@style(box\n**bold** inside\n)'), '<strong>bold</strong>');
+has('macro: block wraps in div', MH('@style(box\ncontent\n)'), '<div class="box">');
+has('macro: block multiple keywords', MH('@style(box center\ncontent\n)'), 'class="box center"');
+
+// Verbatim
+has('macro: verbatim skips markdown', MH('@style(box verbatim\n**bold**\n)'), '**bold**');
+not('macro: verbatim no strong', MH('@style(box verbatim\n**bold**\n)'), '<strong>');
+has('macro: verbatim escapes html', MH('@style(box verbatim\n<b>tag</b>\n)'), '&lt;b&gt;');
+has('macro: verbatim preserves newlines', MH('@style(box verbatim\nline1\nline2\n)'), 'line1<br>');
+not('macro: verbatim keyword stripped', MH('@style(box verbatim\ncontent\n)'), 'verbatim');
+
+// Nesting
+has('macro: inline inside bold', MH('**@npc(Goblin King)**'), '<strong><a href="/NPC/GoblinKing">');
+has('macro: block contains list', MH('@style(box\n- item 1\n- item 2\n)'), '<ul>');
+has('macro: block contains heading', MH('@style(box\n## Title\n)'), '<h2');
+has('macro: inline inside block', MH('@style(box\nhello @user world\n)'), '<a href="/user">TestUser</a>');
+
+// Inside other elements
+has('macro: in list item', MH('- @npc(Goblin King)'), '<a href="/NPC/GoblinKing">');
+has('macro: in heading', MH('## @npc(Goblin King)'), '<a href="/NPC/GoblinKing">');
+
+// Fenced code protection
+not('macro: not in code block', MH('```\n@user\n```'), '<a href="/user">');
+has('macro: literal in code block', MH('```\n@user\n```'), '@user');
+not('macro: not in inline code', MH('`@user`'), '<a href="/user">');
+
+// Edge cases
+has('macro: multiple inline', MH('@npc(Alice) and @npc(Bob)'), 'Alice');
+has('macro: multiple inline second', MH('@npc(Alice) and @npc(Bob)'), 'Bob');
+has('macro: unknown block renders error', MH('@bogus(args\ncontent\n)'), 'ribbit-error');
+
+// Round-trips
+eq('macro: npc round-trip', mrt('@npc(Goblin King)'), '@npc(Goblin King)');
+eq('macro: user round-trip', mrt('hello @user world'), 'hello @user world');
+
 // ── Results ─────────────────────────────────────────────
 const total = passed + failed;
 console.log(`\n${passed}/${total} passed (${Math.round(100 * passed / total)}%) — ${failed} failed`);