Render chat and previews through the shared HTML cleaner

Why: The conversation and office fallbacks wrote marked output straight into the page, including converted docx HTML.
Evidence: html-sinks ratchet forbids new innerHTML writes outside @ui safeHtml.
Impact: Conversation keeps line-break rendering. Unsafe links are stripped after docx and pptx preview. dompurify is deduped with the UI package.
Refs: feature/sillytavern-review
Co-authored-by: Cursor <cursoragent@cursor.com>

test/html-sinks.test.ts

@@ -0,0 +1,29 @@
+// 棘轮：宿主侧的 HTML 写入必须走 @ui safeHtml，不能在组件里直接塞字符串。
+import { describe, expect, it } from 'vitest'
+import { readFileSync, readdirSync, statSync } from 'node:fs'
+import { join, relative, dirname } from 'node:path'
+import { fileURLToPath } from 'node:url'
+
+const SRC = join(dirname(fileURLToPath(import.meta.url)), '..', 'src')
+
+function walk(dir: string, out: string[] = []): string[] {
+  for (const name of readdirSync(dir)) {
+    const p = join(dir, name)
+    if (statSync(p).isDirectory()) walk(p, out)
+    else if (/\.(ts|tsx)$/.test(name)) out.push(p)
+  }
+  return out
+}
+
+describe('html sinks', () => {
+  it('frontend components do not write HTML themselves', () => {
+    const hits: string[] = []
+    for (const file of walk(SRC)) {
+      const text = readFileSync(file, 'utf8')
+      const rel = relative(SRC, file)
+      if (text.includes('dangerouslySetInnerHTML')) hits.push(`${rel}: dangerouslySetInnerHTML`)
+      if (/innerHTML\s*=\s*(?!['"]['"])/.test(text)) hits.push(`${rel}: innerHTML`)
+    }
+    expect(hits).toEqual([])
+  })
+})