chore(release): add changeset for dashboard release

Author: TabishB

.changeset/view-dashboard-slash-support.md

@@ -0,0 +1,7 @@
+---
+"@fission-ai/openspec": minor
+---
+
+- Add an `openspec view` dashboard that rolls up spec counts and change progress at a glance
+- Generate and update AI slash commands alongside the renamed `openspec/AGENTS.md` instructions file
+- Remove the deprecated `openspec diff` command and direct users to `openspec show`