✨ feat: auto-discover Zynq IP after reboot (UART or UDP scan)

After Step 4 reboot, the Zynq may obtain a different IP via DHCP.

IP discovery strategy:
1. UART available → parse IP from boot output (fast, zero network traffic)
2. UART unavailable → scan 192.168.100.11–30 via UDP ver() probe
   (port = last_octet - 3, 0.5s timeout each, ~10s max for 20 IPs)

If IP changed → auto-update config.zynq_ip + UI field

src/gui/main_window.py

@@ -1146,6 +1146,7 @@ class MainWindow(ctk.CTk):
         boot_delay = self._config.boot_wait_delay
         uart_alive = (self._uart_monitor is not None
                       and self._uart_monitor.is_running())
+        discovered_ip: str = ""
         if uart_alive:
             self._log_message(f"  ⏳ Waiting for UART boot signal (max {boot_delay}s)...")
             elapsed = 0.0
@@ -1156,6 +1157,7 @@ class MainWindow(ctk.CTk):
                         f"  ✓ Boot detected after {elapsed:.1f}s"
                         f" (IP={info.ip_address}, Ver={info.version})"
                     )
+                    discovered_ip = info.ip_address
                     break
                 time.sleep(0.5)
                 elapsed += 0.5
@@ -1165,6 +1167,23 @@ class MainWindow(ctk.CTk):
             self._log_message(f"  ⏳ UART unavailable — sleeping {boot_delay}s for boot...")
             time.sleep(boot_delay)
 
+        # Discover actual IP after reboot (may have changed via DHCP)
+        if not discovered_ip:
+            self._log_message("  Scanning for Zynq IP (192.168.100.11–30)...")
+            discovered_ip = self._discover_zynq_ip()
+            if discovered_ip:
+                self._log_message(f"  ✓ Found Zynq at {discovered_ip}")
+            else:
+                self._log_message("  ⚠ Zynq not found on any scanned IP")
+
+        if discovered_ip and discovered_ip != self._config.zynq_ip:
+            self._log_message(
+                f"  IP changed: {self._config.zynq_ip} → {discovered_ip}"
+            )
+            self._config.zynq_ip = discovered_ip
+            if self._ip_string_var:
+                self._ip_string_var.set(discovered_ip)
+
         # 4e: Verify boot
         self._log_message("Step 4e: Verifying boot...")
         if hasattr(self, '_tftp_sub_step_frame'):
@@ -1655,6 +1674,27 @@ class MainWindow(ctk.CTk):
 
         threading.Thread(target=_thread, daemon=True).start()
 
+    def _discover_zynq_ip(self) -> str:
+        """Scan IP range to find the Zynq after reboot.
+
+        Sends UDP ver() to each candidate IP (port = last_octet - 3)
+        and returns the first IP that responds.
+
+        Returns:
+            Discovered IP address, or empty string if not found.
+        """
+        subnet = "192.168.100"
+        for last in range(11, 31):
+            ip = f"{subnet}.{last}"
+            try:
+                from reboot_manager import _send_udp_command
+                ok, _resp = _send_udp_command(ip, b"ver()", timeout=0.5)
+                if ok:
+                    return ip
+            except Exception:
+                continue
+        return ""
+
     # ── Vitis Check ────────────────────────────────────────────
 
     def _check_vitis(self) -> None: