feat(footer): add FAQ modal (@openvaibhav)

[openvaibhav]

Description

Implements the FAQ window requested in #617.

A FAQ button has been added to the footer that opens a modal with two panels:

• Left panel - a list of topics the user can click to navigate
• Right panel - displays the content for the selected topic

A live search box at the top filters topics as you type.
Matching topics are shown instantly based on the title and relevant keywords.

Topics covered

• How to type coding symbols (punctuation mode, quote mode, custom text)
• How to restart the test quickly (Tab + Enter, Quick Restart)
• How to change the language
• How to change the theme
• How to save progress (account system)
• How the leaderboards work
• What Blind Mode is
• What Pace Caret is
• What Funbox modes are
• How to use Custom Text
  [Others can be Added Later]

Checks

• Adding quotes?
  • 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.

Closes #617

[openvaibhav]

Moved the hardcoded FAQ content to a static JSON file (frontend/static/faq.json). The component now fetches it using cachedFetchJson