✨ 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/config_manager.py

@@ -15,7 +15,7 @@ import yaml
 
 
 DEFAULT_CONFIG: dict[str, Any] = {
-    "vitis_path": "",
+    "xilinx_path": "",
     "zynq_ip": "192.168.100.11",
     "tftp_upload_name": "z7bin",
     "serial_port": "",
@@ -52,7 +52,7 @@ class Config:
     directory and resolved to absolute paths when accessed.
     """
 
-    vitis_path: str = ""
+    xilinx_path: str = ""
     zynq_ip: str = "192.168.100.11"
     tftp_upload_name: str = "z7bin"
     serial_port: str = ""
@@ -160,7 +160,7 @@ class Config:
             Dictionary representation of the config.
         """
         data = {
-            "vitis_path": self._relative_path(self.vitis_path),
+            "xilinx_path": self.xilinx_path,
             "zynq_ip": self.zynq_ip,
             "tftp_upload_name": self.tftp_upload_name,
             "serial_port": self.serial_port,