Update color surfaces to canvas in repo UI.

Diff code block container background.

README code and preview backgrounds.

Commit view header background.

Looks good — straightforward fix for the code block background color.

use canvas background for readme and commit header

Refine hover surface colors

Match file header background to canvas

Refine hover surface colors

Match file header background to canvas

Simplify outline button hover styling

Swap light-mode seed button colors

Adjust seed button and counter colors in light theme

Simplify seed color override with per-instance button class

Unify tab hover with outline button hover

Revert SeedButton color overrides

Remove Button className passthrough

Move cob header background style to shared component

Align source and diff selected backgrounds

This generally fixes a few places that just looked broken in the app. Weird uses of the primary color, muddy hover states on buttons, border colors that weren’t displaying right.

style: add hover state for selected file rows

style: darken selected file row state