Improve: give widget cards the iOS 27 edge light and headings

[SandObserver]

Summary

• Draw the kit's edge light on widget cards through a ::after layer above the frame, pinned to its own compositing layer so it does not appear late after a page change on iOS.
• Add --card-edge-hi and --card-edge-lo for both themes, and keep the dark values on widgets held dark in the light theme.
• Set the Books, DNS and VPN headings in semibold mixed case at 11 to 13, replacing tracked uppercase.
• Change the Books shelf names in the en, de, es and fr catalogs and their fallbacks from uppercase to each language's normal casing.

Testing
All green, including Docker build and e2e. Added a check that widgets held dark keep the dark edge light.

Changelog

Changed

• Give widget cards the iOS 27 edge light and drop the uppercase widget headings.

Checklist

• Stays within the project constraints: one container, no runtime dependencies, no build step (see CONTRIBUTING.md).
• Tests added or updated for new logic, and the full suite, lint, and typechecks pass.
• Docs updated if behavior or configuration changed.