Gradient tool does not fade into transparency
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#### Summary:
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The gradient tool produces a 'solid gradient' instead of fading into transparency. Introduced in https://gitlab.com/inkscape/inkscape/-/commit/87dff623b094a526f8cac371fa65a92514131cd7. Switching to a 'Gradient' using the Fill&Stroke dialog also has the same regression.
#### Steps to reproduce:
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- open Inkscape
- Create an object with a fill
- Add a gradient using the gradient tool
#### What happened?
Object has a gradient, but it isn't obvious
#### What should have happened?
Same behaviour as 1.4.2 - gradient fading into transparency.
#### Version info
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```
Inkscape 1.5-dev (b56c385615, 2025-09-26, custom)
Compile (Run)
GLib version: 2.84.4
GTK version: 4.18.6 (4.18.6)
glibmm version: 2.83.1
gtkmm version: 4.18.0
libxml2 version: 2.12.10
libxslt version: 1.1.43
Cairo version: 1.18.2 (1.18.2)
Pango version: 1.56.4 (1.56.4)
HarfBuzz version: 10.4.0 (10.4.0)
Poppler version: 25.02.0
OS version: Fedora Linux 42 (Workstation Edition)
```
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issue