docs: deprecate GUI V6, update docs for FT2232H production default

- Add deprecation headers to GUI_V6.py and GUI_V6_Demo.py
- Mark V6 as deprecated in GUI_versions.txt
- Update README.md: replace V6 GIF reference with V65 PNG
- Add FT2232H production notice banner to docs/index.html

docs/index.html

@@ -32,6 +32,11 @@
     </section>
 
     <section class="stats-grid">
+      <article class="card stat notice">
+        <h2>Production Board USB</h2>
+        <p class="metric">FT2232H (USB 2.0)</p>
+        <p class="muted">50T production board uses FT2232H. FT601 USB 3.0 is available on 200T premium dev board only.</p>
+      </article>
       <article class="card stat">
         <h2>Tracked Timing Baseline</h2>
         <p class="metric">WNS +0.058 ns</p>