Fix esptool skip condition to use shutil.which

The test was hardcoded to check /usr/bin/esptool, but esptool lives
in ~/.local/bin/ on this system. Use shutil.which() to properly
search PATH.

tests/test_config.py

@@ -3,6 +3,7 @@ Test configuration management
 """
 
 import os
+import shutil
 from pathlib import Path
 
 import pytest
@@ -74,11 +75,10 @@ def test_common_ports():
     assert len(ports) > 0  # Should return some ports for any platform
 
 
-@pytest.mark.skipif(not Path("/usr/bin/esptool").exists(), reason="esptool not found")
+@pytest.mark.skipif(not shutil.which("esptool"), reason="esptool not found in PATH")
 def test_tool_availability():
     """Test tool availability check"""
     config = ESPToolServerConfig()
 
-    # This should work if esptool is in PATH
     available = config._check_tool_availability("esptool")
-    assert isinstance(available, bool)
+    assert available is True