Black text on black background for several themes

## Description
Black text on a black background is hardly readable

## Steps to reproduce

1. MacOS 15.5, codewhale 0.9.13
2. Themes (at least): gruvbox-dark, underwater, maybe more of them
3. Some screens contain fully black text on a black background

It's better to change color appearance to make text more readable

## Expected behavior
Good text readability

## Actual behavior
Very poor readability of some text parts

## Impact
At least the following screens suffer:
/plugin enable
/setup

/context -> some subfolder, eg messages:

## Environment

- OS: MacOS 15.5
- codewhale version: 0.9.13
- Install method: brew install
- `codewhale doctor` summary: all ok
- Model/provider: google/gemini (but it seems more a problem with codewhale itself)
- Terminal app: Terminal
- Shell: zch

## Logs, screenshots, or recordings
See above

Start by reproducing the issue on macOS 15.5 with codewhale 0.9.13 in the gruvbox-dark and underwater themes, checking /plugin enable, /setup, and /context in a terminal. No files or tests are named; trace those screens to their theme and text-color definitions, then verify that the affected text has readable contrast across the reported screens.

Written by the indexing model from the issue text.