Fix time server to default to UTC when tzinfo is unavailable (#2738)

When get_localzone_name() returns None, the server now defaults to UTC
instead of raising an error. This makes the server more robust in
environments where the local timezone cannot be determined.

src/time/src/mcp_server_time/server.py

@@ -46,7 +46,8 @@ def get_local_tz(local_tz_override: str | None = None) -> ZoneInfo:
     local_tzname = get_localzone_name()
     if local_tzname is not None:
         return ZoneInfo(local_tzname)
-    raise McpError("Could not determine local timezone - tzinfo is None")
+    # Default to UTC if local timezone cannot be determined
+    return ZoneInfo("UTC")
 
 
 def get_zoneinfo(timezone_name: str) -> ZoneInfo:

src/time/test/time_server_test.py

@@ -486,10 +486,10 @@ def test_get_local_tz_with_valid_iana_name(mock_get_localzone):
 
 @patch('mcp_server_time.server.get_localzone_name')
 def test_get_local_tz_when_none_returned(mock_get_localzone):
-    """Test error when tzlocal returns None."""
+    """Test default to UTC when tzlocal returns None."""
     mock_get_localzone.return_value = None
-    with pytest.raises(McpError, match="Could not determine local timezone"):
-        get_local_tz()
+    result = get_local_tz()
+    assert str(result) == "UTC"
 
 
 @patch('mcp_server_time.server.get_localzone_name')