feat: add admin operations documentation and scripts for server management (#323)

## Summary
- Added comprehensive admin operations documentation
- Included scripts for common server management tasks

Together with #315, #316, this fixes #182

tools/admin/takedown.sh

@@ -0,0 +1,17 @@
+#!/bin/bash
+# Simple takedown script
+
+REGISTRY_URL="${REGISTRY_URL:-https://registry.modelcontextprotocol.io}"
+
+if [ -z "$SERVER_ID" ] || [ -z "$REGISTRY_TOKEN" ]; then
+    echo "Usage: REGISTRY_TOKEN=<token> SERVER_ID=<server-uuid> $0"
+    exit 1
+fi
+
+# Get current server and update status to deleted
+curl -s "${REGISTRY_URL}/v0/servers/${SERVER_ID}" | \
+jq '.status = "deleted" | {server: .}' | \
+curl -X PUT "${REGISTRY_URL}/v0/servers/${SERVER_ID}" \
+  -H "Authorization: Bearer ${REGISTRY_TOKEN}" \
+  -H "Content-Type: application/json" \
+  -d @-