feat: print to discovered printer IP

print_receipt now resolves the printer by MAC via discover_printer() instead of
a hardcoded IP. Verified end-to-end: physical receipt printed to 192.168.0.184.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

pos_briefing.py

@@ -504,9 +504,14 @@ def discover_printer():
 
 def print_receipt(raw_bytes):
     try:
-        with socket.create_connection((PRINTER_IP, PRINTER_PORT), timeout=10) as sock:
+        ip = discover_printer()
+    except Exception as e:
+        print(f"[!] Printer discovery failed: {e}")
+        return False
+    try:
+        with socket.create_connection((ip, PRINTER_PORT), timeout=10) as sock:
             sock.sendall(raw_bytes)
-        print(f"✓ Receipt sent to {PRINTER_IP}:{PRINTER_PORT}")
+        print(f"✓ Receipt sent to {ip}:{PRINTER_PORT}")
         return True
     except Exception as e:
         print(f"[!] Print failed: {e}")