✨ feat: Xilinx Kit directory selector + multi-version scan

Configuration panel now has a 'Xilinx Kit:' row at the top with:
- Entry field showing current path
- [Browse] button using system directory dialog (cross-platform)
- Select root directory (e.g. /data/xilinx or C:/Xilinx)

vitis_checker.py now scans xilinx_root subdirectories:
  1. System PATH (shutil.which) — works on all platforms
  2. Legacy vitis_path/bin
  3. xilinx_root/Vitis/*/bin and Vivado/*/bin (all versions, newest first)
  4. Common install paths (Windows: C:/Xilinx, Linux: /data/xilinx, /opt/xilinx)

Multi-version: scans all version directories under Vitis/ and Vivado/,
picks the newest version for each tool.

Config: xilinx_path replaces vitis_path (backward compat kept)

src/flash_programmer.py

@@ -112,7 +112,10 @@ def wipe_flash(
     Returns:
         FlashResult with status.
     """
-    flash_tool = get_program_flash_path(config.vitis_path)
+    flash_tool = get_program_flash_path(
+        vitis_path=config.vitis_path if hasattr(config, 'vitis_path') else "",
+        xilinx_root=config.xilinx_path if hasattr(config, 'xilinx_path') else "",
+    )
     if not flash_tool:
         return FlashResult(
             step="wipe",
@@ -225,7 +228,10 @@ def program_flash_bin(
             message=f"BIN file not found: {bin_path}",
         )
 
-    flash_tool = get_program_flash_path(config.vitis_path)
+    flash_tool = get_program_flash_path(
+        vitis_path=config.vitis_path if hasattr(config, 'vitis_path') else "",
+        xilinx_root=config.xilinx_path if hasattr(config, 'xilinx_path') else "",
+    )
     if not flash_tool:
         return FlashResult(
             step="program",