[BUG] Custom style.css ignored unless ~/.config/nmrs/theme is removed

[pwsandoval]

Describe the bug
Custom style.css is ignored when a theme is selected.
The custom stylesheet located at:

~/.config/nmrs/style.css

only takes effect after removing or renaming the saved theme file:

~/.config/nmrs/theme

If the theme file exists, the UI always loads the predefined theme instead of the custom stylesheet.

What should happen?:
Custom style.css should override the selected theme, or the theme selector should reflect that a custom stylesheet is active (e.g. showing Custom).

Additional context
Environment:

• Fedora KDE
• Hyprland
• nmrs-gui built from source (cargo build --release)

Steps to reproduce:

1. Create ~/.config/nmrs/style.css with custom styles.
2. Ensure ~/.config/nmrs/theme exists (e.g. catppuccin).
3. Start nmrs-gui.

Result: custom CSS is ignored.

After removing the theme file:

mv ~/.config/nmrs/theme ~/.config/nmrs/theme.bak

the custom stylesheet is applied correctly.