Add changeset for config command and shell completions (#388)

Author: TabishB

.changeset/config-and-completions.md

@@ -0,0 +1,18 @@
+---
+"@fission-ai/openspec": minor
+---
+
+### New Features
+- Add `openspec config` command for managing global configuration settings
+- Implement global config directory with XDG Base Directory specification support
+- Add Oh-my-zsh shell completions support for enhanced CLI experience
+
+### Bug Fixes
+- Fix hang in pre-commit hooks by using dynamic imports
+- Respect XDG_CONFIG_HOME environment variable on all platforms
+- Resolve Windows compatibility issues in zsh-installer tests
+- Align cli-completion spec with implementation
+- Remove hardcoded agent field from slash commands
+
+### Documentation
+- Alphabetize AI tools list in README and make it collapsible