fix: add missing Ngspice v40 to GUI version dropdown in gui_fixed.py

[Eashan-H]

Related Issues

Found while testing feature/tool-manager-integration on Windows.

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Purpose

Ngspice version 40 is missing from the version dropdown in gui_fixed.py. The list jumps from 39 directly to 41, so users cannot select or install Ngspice 40 from the GUI even though the backend tool_manager_windows.py fully supports it.

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Approach

Added "40" to the versions list in gui_fixed.py to match the backend NGSPICE_VERSIONS dict which already has version 40 defined:

# Before
"versions": ["latest", "35", "36", "37", "38", "39", "41", "42"]

# After
"versions": ["latest", "35", "36", "37", "38", "39", "40", "41", "42"]