updated: removed gradient from onboarding buttons (#5178)

Fixes #5168

- Added primaryInverted and primaryInvertedHover to design system.
- Changed primary button background with a gradient to inverted-flat for
both light and dark themes.
- Hover added to go lighter (consistent with tertiary color of +5 step
on GRAY_SCALE).
- Font color changed from primary to inverted.
- Modified button border from light to strong.

Two components are still utilizing the button with gradient background -
email and chrome extension.
Figma design guidelines show them to be inverted and flat (not
gradient).

- Should I change those as well?
- Should the gradient style be removed altogether after this has been
completed?

Co-authored-by: Henry Kim <henrykim@Henrys-iMac.local>

packages/twenty-docs/src/ui/generated/index.d.cts

@@ -37,6 +37,8 @@ declare const lightTheme: {
         overlay: string;
         radialGradient: string;
         radialGradientHover: string;
+        primaryInverted: string;
+        primaryInvertedHover: string;
     };
     border: {
         radius: {