fix(vitis): add xsct fallback for impact detection in Xilinx 2023.2

- vitis_checker: shutil.which() + xsct fallback for impact detection
- flash_programmer: _get_impact_path now checks xsct as fallback
- bitstream_programmer: _get_impact_path now checks xsct as fallback
- GUI: show '(via xsct)' alias note when xsct replaces impact
- ToolStatus: add 'alias' field for tracking which executable was found

src/gui/main_window.py

@@ -487,7 +487,8 @@ class MainWindow(ctk.CTk):
 
         for tool_name, tool_info in status_dict["tools"].items():
             if tool_info["found"]:
-                self._log_message(f"    ✓ {tool_name}: {tool_info['path']}")
+                alias_note = f" (via {tool_info['alias']})" if tool_info.get("alias") and tool_info["alias"] != tool_name else ""
+                self._log_message(f"    ✓ {tool_name}: {tool_info['path']}{alias_note}")
             else:
                 self._log_message(f"    ✗ {tool_name}: {tool_info['error']}")