fix: resolve 18 QA-discovered bugs across tools, previews, and the AI pipeline (#242)

Exhaustive QA sweep of all 157 tools. Fixes: CSP blob media, csv-excel ExcelJS interop, ocr-pdf segfault, chart-maker upload, non-PDF doc preview, RAW decode, merge-tool multi-file path, html-to-image chromium, ogv/wma/amr/ac3 preview fallbacks, meme/gif/stabilize codecs, nav+home a11y. Plus orphan-format and test-debt cleanup, the AI bundle build script, and a reusable Playwright QA harness under tests/qa/.

apps/web/src/pages/home-page.tsx

@@ -119,6 +119,7 @@ export function HomePage() {
   return (
     <AppLayout>
       <div>
+        <h1 className="sr-only">{t.homePage.heading}</h1>
         <div className="mx-auto max-w-6xl px-4 py-8 sm:px-6 lg:px-8">
           <HomeSearchBar
             value={search}