Mispelled and unknown words are difficult to read with Dark and System themes

[TraceyC77]

Describe the bug

In a recent update, Nheko began automatically highlighting misspelled / unknown words (technical terms, words in another language etc)
The low contrast this text has in the Dark & System Nheko themes makes any affected text hard to read.
This is an accessibility issue.

Additionally, words are highlighted as misspelled before the user is finished typing them, which makes this more of an issue.

There isn't a setting to disable spellcheck, so there is no ability for the user to work around this except to use the Light theme.

This relates to an old feature request /issues/174
Just underlining misspelled / not yet complete / unknown words would be more readable than making the text red on a red background.

To Reproduce

1. Set Nheko to use the Dark theme or use System, with the system theme set to a dark theme.
2. Start typing in the input area. Stop before you complete a word or misspell a word to trigger the spell check

Note that with my settings, the input area when using System (dark grey) is darker than Dark (medium grey)
I've attached screenshots using both themes

What happened?

The text is red, with a red underline and a translucent red background against the grey input area.
The misspelled word is difficult to read, due to low contrast between colors. Regular text is easy to read.
Spellcheck errors are triggered on words that are still being typed.

Expected behavior

Misspelled / unknown words are as easy to read as default text
Spell check is not triggered until a space is typed, indicating the word is done being entered

Screenshots

Dark theme

System theme

Version

0.12.0

Operating system

Linux

Installation method

Some repository (AUR, homebrew, distribution repository, PPA, etc)

Qt version

6.7.2

C++ compiler

No response

Desktop Environment

KDE Plasma

Did you use profiles?

• Profiles used?

Relevant log output

No response

Backtrace

No response