Introduce dark mode for the portal

[ooaklee]

SUMMARY

This ticket to add dark mode to the portal depends on #14 . Once that is introduced, we can work on managing the implementation logic of switching between themes. The portal uses tailwindcss for styling, so you could opt to manage the switching of themes using the tailwind config https://github.com/boasiHQ/interactive-inputs/blob/main/src/internal/web/ui/static/css/tailwind-base.css

SUCCESS CRITERIA

• Add a new option to valid theme names to include "dark"
• Update logic to switch between themes will have to consider the following:
  • https://github.com/boasiHQ/interactive-inputs/blob/main/src/internal/web/ui/html/pages/%40landing.tmpl.html
  • https://github.com/boasiHQ/interactive-inputs/blob/main/src/internal/web/ui/html/partials/responses/cancel.tmpl.html
  • https://github.com/boasiHQ/interactive-inputs/blob/main/src/internal/web/ui/html/partials/responses/success.tmpl.html
• Add screenshots/gifs of the portal in dark mode