fix: Define every token the theme uses and make all UI Skins variables editable

Problem/Motivation

Nine UIkit tokens were used but never defined, so the delete and icon buttons failed contrast on hover. Two UI Skins variables could not be edited, there were no dark defaults, and an accent set in the theme settings silently beat UI Skins.

Proposed resolution

• Define every token, light and dark.
• Expose all tokens in UI Skins with descriptions and light and dark defaults.
• Store the accent and focus colors once, in UI Skins, with a separate dark accent.
• Turn the sizes and corner radii into tokens.
• Fix the shell defects found in testing: the Inaccessible rail item, the sticky table header, the phone drawer, missing command palette items, pink emphasis.

Remaining tasks

• ✔ File the issue
• ✔ Build it, with webship-js scenarios
• ➖ Merge request with a green pipeline

User interface changes

N/A

API changes

N/A

Data model changes

Accent and focus move to UI Skins, with a post update.

AI-Generated: Yes