fix(ui): normalize Tk padding values

[2002yy]

What changed

• normalize the bottom ttk padding value to a Python int before adding it to the computed content height

Why

The current Windows 2025/Tk runner returns ttk padding elements as _tkinter.Tcl_Obj. _calc_content_height() added that object directly to an int, causing 17 GUI smoke tests to fail at application construction with TypeError.

The frame padding is constructed from integer constants, so int(str(pad[3])) preserves the existing layout value while making the calculation independent of Tk's Python wrapper type.

This keeps the GUI tests fail-closed; no runner pinning, skipping, or continue-on-error workaround is added.

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