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

9_Firmware/9_3_GUI/GUI_V6.py

@@ -1,3 +1,9 @@
+# =============================================================================
+# DEPRECATED: GUI V6 is superseded by GUI_V65_Tk (tkinter) and V7 (PyQt6).
+# This file is retained for reference only. Do not use for new development.
+# Removal planned for next major release.
+# =============================================================================
+
 import tkinter as tk
 from tkinter import ttk, messagebox
 import threading

9_Firmware/9_3_GUI/GUI_V6_Demo.py

@@ -1,5 +1,11 @@
 #!/usr/bin/env python3
 
+# =============================================================================
+# DEPRECATED: GUI V6 Demo is superseded by GUI_V65_Tk and V7.
+# This file is retained for reference only. Do not use for new development.
+# Removal planned for next major release.
+# =============================================================================
+
 """
 Radar System GUI - Fully Functional Demo Version
 All buttons work, simulated radar data is generated in real-time

9_Firmware/9_3_GUI/GUI_versions.txt

@@ -6,7 +6,7 @@ GUI_V4 ==> Added pitch correction
 
 GUI_V5 ==> Added Mercury Color
 
-GUI_V6 ==> Added USB3 FT601 support
+GUI_V6 ==> Added USB3 FT601 support  [DEPRECATED — superseded by V65/V7]
 
 GUI_V65_Tk ==> Board bring-up dashboard (FT2232H reader, real-time R-D heatmap, CFAR overlay, waterfall, host commands, HDF5 recording, replay, demo mode)
 radar_protocol ==> Protocol layer (packet parsing, command building, FT2232H connection, data recorder, acquisition thread)