Improvements and Fixes to Dark Mode

[Ashesh3]

Important

Dark mode was temporarily disabled in #193 ; Make sure to enable it first in src/components/sidebar/chatSidebar.tsx

• Test results, PDF download: better to have it in light mode with white background (good to have). the title of the PDF is not visible as the text is in light grey in white background. Formatting of the PDF may be improved. [ Refer to video from 19:50 min. ]

• Change the light grey text in feedback and selections (language/project) to black for better visibility.
  

• Fix issues in UI elements like buttons and text fields that affect usability. (example: button at top right of project page)
  

• Users page
  

• User edit page
  

• Test run page text, dropdown and attachment button
  

• Test result
  

• Cancel button in delete chat confirmation