Decision Log: Fix responsive layout and spacing in archived toggle header

Summary

Follow-up from the UX review of !256580 (merged) (Add archived decision toggle and update count). Two minor UI polish items were identified after merge.

Issues

1. Responsive layout on small devices

On small (XS) viewports, the decision log panel header does not reflow correctly — elements overflow without wrapping. The XS layout variant was included in the Figma design but was not specifically called out in the issue. No wrapping is currently set, causing things to look broken at narrow widths.

2. Gap between header elements

The gap between the primary action button and the "Show archived" toggle should be 16px / 1rem rather than the current 8px. The larger gap creates clearer visual separation between the primary action and the toggle (which itself already has an 8px margin between its label and control).

References

• Follow-up from !256580 (merged)
• Related to #629493 (closed)