Add a table-insert toolbar button to the markdown editor (#109)

The markdown toolbar offered bold/italic/code/heading/list/quote/link
but no table option, despite README describing table rendering as a
supported feature — the parser already renders manually-typed table
syntax correctly, this was purely a discoverability gap for a user who
wouldn't otherwise know the exact `| Header | Header |` / `|---|---|`
syntax to type from scratch.

Added toolbarTable(), which inserts a 2-column starter template (with
a leading newline only when needed, matching the table syntax's
requirement of a full line to itself) matching exactly what
parseMarkdownTables()'s detection regex expects, wired into the
toolbar's existing data-toolbar-action dispatch. Verified via jsdom
that the inserted template parses into a real HTML table.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Lhz7pGMaoTfL5sdYS5XiKv

assets/js/markdown.js

@@ -506,6 +506,25 @@ function toolbarHeading(textareaId) {
     textarea.dispatchEvent(new Event('input', { bubbles: true }));
 }
 
+function toolbarTable(textareaId) {
+    const textarea = document.getElementById(textareaId);
+    if (!textarea) return;
+
+    const start = textarea.selectionStart;
+    const text = textarea.value;
+
+    // Insert on its own line(s), matching the blank-line-before convention
+    // toolbarList/toolbarHeading rely on the surrounding text for — a table
+    // needs a full line to itself both before and after the separator row.
+    const needsLeadingNewline = start > 0 && text[start - 1] !== '\n';
+    const template = (needsLeadingNewline ? '\n' : '')
+        + '| Header 1 | Header 2 |\n'
+        + '| --- | --- |\n'
+        + '| Cell 1 | Cell 2 |\n';
+
+    insertMarkdownText(textareaId, template);
+}
+
 function toolbarQuote(textareaId) {
     const textarea = document.getElementById(textareaId);
     if (!textarea) return;
@@ -544,6 +563,7 @@ function createEditorToolbar(textareaId, containerId) {
         <button type="button" data-toolbar-action="heading" data-textarea="${textareaId}" title="Heading">H</button>
         <button type="button" data-toolbar-action="list" data-textarea="${textareaId}" title="List">≡</button>
         <button type="button" data-toolbar-action="quote" data-textarea="${textareaId}" title="Quote">"</button>
+        <button type="button" data-toolbar-action="table" data-textarea="${textareaId}" title="Table">▦</button>
         <span class="toolbar-separator"></span>
         <button type="button" data-toolbar-action="link" data-textarea="${textareaId}" title="Link">[ @ ]</button>
     `;
@@ -563,6 +583,7 @@ function createEditorToolbar(textareaId, containerId) {
             case 'heading': toolbarHeading(targetId); break;
             case 'list': toolbarList(targetId); break;
             case 'quote': toolbarQuote(targetId); break;
+            case 'table': toolbarTable(targetId); break;
             case 'link': toolbarLink(targetId); break;
         }
     });
@@ -578,6 +599,7 @@ window.toolbarLink = toolbarLink;
 window.toolbarList = toolbarList;
 window.toolbarHeading = toolbarHeading;
 window.toolbarQuote = toolbarQuote;
+window.toolbarTable = toolbarTable;
 window.createEditorToolbar = createEditorToolbar;
 window.insertMarkdownFormat = insertMarkdownFormat;
 window.insertMarkdownText = insertMarkdownText;