docs: release alpha 3 — remove in-progress marker, fix export description

Mark Alpha 3 as released (drop the "in progress" qualifier) and correct
the bidirectional format export entry: only LaTeX ↔ Typst conversion is
available; DOCX, Markdown and HTML exports are not yet implemented.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

@@ -135,7 +135,7 @@ Refinements to the Typst editor and the format badge system:
   shortcuts (`Ctrl+B`, `Ctrl+I`), plus underline, small-caps and hyperlink
   buttons, matching the Quarto and LaTeX toolbar experience.
 
-### Alpha 3 *(in progress)*
+### Alpha 3
 
 - **Lumière theme** — redesigned project dashboard with a card grid, PDF/slide
   thumbnails, parallax hover effects, a teal gradient identity and a dark editor
@@ -146,9 +146,8 @@ Refinements to the Typst editor and the format badge system:
   shortcuts in the toolbar for `.qmd` and `.typ` files.
 - **Top/bottom split view** — new editor layout that stacks the source editor
   above the PDF preview vertically, in addition to the existing side-by-side mode.
-- **Bidirectional format export** — LaTeX projects can be exported to Typst,
-  DOCX, Markdown or HTML via pandoc; Typst projects can be exported to LaTeX.
-  Available from the File menu in the editor.
+- **Bidirectional format export** — LaTeX projects can be converted to Typst and
+  Typst projects to LaTeX via pandoc. Available from the File menu in the editor.
 - **Mobile layout** — project dashboard, search bar, footer and editor all
   adapted for phone screen sizes.