Add changeset for bulk-archive skill and setup simplification (#540)

Author: TabishB

.changeset/bulk-archive-and-setup.md

@@ -0,0 +1,11 @@
+---
+"@fission-ai/openspec": minor
+---
+
+### New Features
+
+- **Bulk archive skill** — Archive multiple completed changes in a single operation with `/opsx:bulk-archive`. Includes batch validation, spec conflict detection, and consolidated confirmation
+
+### Other
+
+- **Simplified setup** — Config creation now uses sensible defaults with helpful comments instead of interactive prompts