Renames the `--border-hover` design token to `--border-secondary` and
updates the color values to work well on `surface-secondary`
backgrounds, preparing for the template creation flow.
- Light theme: `240 5% 65%` (`#A1A1AA`)
- Dark theme: `240 5% 26%` (`#3F3F46`)
All 7 component usages updated to use the new token name.
<details>
<summary>Context</summary>
The previous `border-hover` token used a single value (`#52525B`) for
both themes, which didn't provide enough contrast on `surface-secondary`
backgrounds. The rename to `border-secondary` better reflects its
semantic role as a secondary border color rather than a hover-specific
one, and the updated values give proper contrast in both light and dark
themes. This change is a prerequisite for the upcoming template creation
flow work.
</details>
> 🤖 Generated by Coder Agents
christin