feat(theme): add dusty_plum theme (@iamanuclearwarhead)

[iamanuclearwarhead]

Description

Adds a new theme called dusty plum, since i wanted a dark theme with a muted plum background and a soft pastel pink for the caret and highlights, cus a lot of the existing pink themes are saturated

Colors

• bg #41283d, main/caret #f2a6c6, sub #9a6f92, text #fbeaf3
• error uses a coral pink so it still stands out from the text
• colorful error uses a pastel orange so wrong letters are clearly different from the pink correct letters when colorful mode is on

Checked readability with flip test colors and colorful mode on and off, screenshots below.

default

colorful mode

flip test colors

flip + colorful

Checks

• Adding quotes?
  • Make sure to follow the quotes documentation
  • Make sure to include translations for the quotes in the description (or another comment) so we can verify their content.
• Adding a language?
  • Make sure to follow the languages documentation
  • Add language to packages/schemas/src/languages.ts
  • Add language to exactly one group in frontend/src/ts/constants/languages.ts
  • Add language json file to frontend/static/languages
• Adding a theme?
  • Make sure to follow the themes documentation
  • Add theme to packages/schemas/src/themes.ts
  • Add theme to frontend/src/ts/constants/themes.ts
  • (optional) Add theme css file to frontend/static/themes
  • Add some screenshots of the theme, especially with different test settings (colorful, flip colors) to your pull request
• Adding a layout?
  • Make sure to follow the layouts documentation
  • Add layout to packages/schemas/src/layouts.ts
  • Add layout json file to frontend/static/layouts
• Adding a font?
  • Make sure to follow the fonts documentation
  • Add font file to frontend/static/webfonts
  • Add font to packages/schemas/src/fonts.ts
  • Add font to frontend/src/ts/constants/fonts.ts
• Check if any open issues are related to this PR; if so, be sure to tag them below.
• Make sure the PR title follows the Conventional Commits standard. (https://www.conventionalcommits.org for more info)
• Make sure to include your GitHub username prefixed with @ inside parentheses at the end of the PR title.