feat: add markdown-tree integration for document sharding

- Add markdownExploder setting to core-config.yml
- Update shard-doc task to use md-tree command when enabled
- Implement proper fallback handling when tool is unavailable
- Update core-config structure to remove nested wrapper
- Fix field naming to use camelCase throughout

.vscode/settings.json

@@ -24,6 +24,7 @@
 		"Immer",
 		"implementability",
 		"Inclusivity",
+		"kayvan",
 		"Luxon",
 		"MERN",
 		"mgmt",