Update legacy KAUI styles to use blue theme color

[tungleduyxyz]

Summary

This PR updates legacy KAUI styling in element.css to use blue in place of older teal color values.
Related issue: killbill/killbill-admin-ui#648

Changes

• Updated link color to blue
• Updated primary button background to blue
• Updated toggler star color to blue
• Updated checked slider background colors to blue (switch and switch-half)
• Updated spinner color to blue
• Updated active tenant switch color to blue
• Removed custom hover color override for links so hover inherits default color behavior

Scope

• 1 file changed
• 8 insertions, 9 deletions

Testing

• Visual verification recommended in KAUI pages where links, buttons, toggles, and spinner are displayed
• No JavaScript or backend changes

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• app/assets/stylesheets/assets/element.css: Generated file

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