🐛 fix: Step 1 JTAG check uses shared vivado path finder + build_tool_command

Root cause (2 bugs):
1. check_zynq_jtag() used config.vitis_path which no longer exists
   (config now uses xilinx_path) → always got empty path → 'Vivado not found'
2. _get_vivado_path() only checked hardcoded Linux paths, no version
   scanning, no .bat support on Windows

Fix:
- Added get_vivado_path() in vitis_checker.py (consistent with
  get_xsct_path, get_program_flash_path, etc.)
- Uses _find_executable() shared logic: scans Vivado/*/bin +
  Vitis/*/bin, picks newest version, supports .bat on Windows
- zynq_checker.py now uses get_vivado_path() + build_tool_command()
  for proper environment setup (settings64 sourcing on Linux)
- Removed obsolete _get_vivado_path() + unused shutil import

src/vitis_checker.py

@@ -317,6 +317,19 @@ def get_bootgen_path(vitis_path: str = "", xilinx_root: str = "") -> str | None:
     return _find_executable("bootgen", vitis_path, platform.system().lower(), xilinx_root)
 
 
+def get_vivado_path(vitis_path: str = "", xilinx_root: str = "") -> str | None:
+    """Find the Vivado executable (JTAG operations via hw_server).
+
+    Args:
+        vitis_path: Legacy Vitis installation directory.
+        xilinx_root: Xilinx root directory.
+
+    Returns:
+        Path to vivado executable, or None.
+    """
+    return _find_executable("vivado", vitis_path, platform.system().lower(), xilinx_root)
+
+
 # ── Tool version detection ───────────────────────────────────────────