feat: validate JTAG Zynq part matches config.zynq_part (default XC7Z100)

Step 1 now compares detected part (e.g. XC7Z035) against config's
zynq_part. If mismatch: log error, return False to block subsequent
steps. Also returns False when no Zynq detected (was always True).

src/config_manager.py

@@ -17,6 +17,7 @@ import yaml
 DEFAULT_CONFIG: dict[str, Any] = {
     "xilinx_path": "",
     "zynq_ip": "192.168.100.11",
+    "zynq_part": "XC7Z100",
     "tftp_upload_name": "z7bin",
     "serial_port": "",
     "serial_baudrate": 115200,
@@ -55,6 +56,7 @@ class Config:
 
     xilinx_path: str = ""
     zynq_ip: str = "192.168.100.11"
+    zynq_part: str = "XC7Z100"
     tftp_upload_name: str = "z7bin"
     serial_port: str = ""
     serial_baudrate: int = 115200