feat: design tokens - [INS-1482]

[CurryYangxx]

Background: https://konghq.atlassian.net/wiki/spaces/ST/pages/4940497645/Build+Insomnia+Design+System

Changes

Define design tokens:

This is not the final version, will discuss with Missy further

• colors (able to reference tailwind color palette)
• spacing
• radius
• typography

Generate css variables by style-dictionary

Next step:

• integrate with Tailwind( upgrading to v4 will avoid extra work, but it will not be a blocker )

[gatzjames]

To avoid extra work I'd suggest upgrading to tailwind v4 first and defining the tokens in the new css config.
We can also benefit greatly if we extend tailwind's default theme by getting autocomplete suggestions and documentation on hover of each classname

[jackkav]

#9200

There is some risk updating tailwind to v4 but it appears related to this effort, so help getting it updated is very welcome @CurryYangxx

[CurryYangxx]

Thanks for the feedback @jackkav @gatzjames . I will take a look at Tailwind v4 and try to update.

[CurryYangxx]

use '_' instead