Decision Log: Add visibility toggle for archived decisions
Summary
Add a toggle to show/hide archived decisions in the decision log. The toggle should be off by default (archived decisions hidden).
Context
Follow-up from #629243 (closed), originally raised in !255340 (merged).
Design
Acceptance Criteria
- A toggle control is available in the decision log UI to show/hide archived decisions
- The toggle defaults to "off" (archived decisions are hidden by default)
- When toggled on, archived decisions are visible in the log
- When toggled off, archived decisions are hidden