feat(ui): streamline workspace settings and remove sharing

Unify compact workspace controls and panel transitions, move directory actions into the context menu, and remove backlink UI.

Reorganize settings with searchable sections, per-setting resets, shortcut search, and accurate save feedback.

Remove sharing UI, APIs, authentication helpers, and storage code; provide a transactional cleanup script with retirement tests. Reject directories during orphan image cleanup and cover mixed-batch preservation.

web/src/markdown/html.ts

@@ -462,7 +462,7 @@ export function renderMarkdown(src: string, { parser = markdownParser, unsafe =
         const name = text(label.from + 2, label.to - 2)
         return `<div class="footnote" id="${escapeAttr(footnoteId(name))}"><sup>${escapeHtml(name)}</sup> ${inline(node, label.to, node.to).trim()}</div>\n`
       }
-      // 目录占位，由分享页根据标题填充
+      // 目录占位，由调用方根据标题填充
       case 'TableOfContents':
         return '<nav class="toc"></nav>\n'
       // front matter 是元数据，不输出