feat: add elasticsearch-mcp validation

Build and validate Elasticsearch MCP server for search/indexing.

Changes:
- docker-compose.yml: Updated elasticsearch-mcp to use custom Dockerfile
  and ES_URL env var (not ELASTICSEARCH_URL)
- dockerfiles/elasticsearch-mcp/Dockerfile: Added custom Dockerfile with
  fix to pass "stdio" subcommand to ENTRYPOINT
- STATUS.md: Added elasticsearch-mcp as validated MCP (v0.2.1, 22MB)

Validation:
- Container builds successfully from Rust source (22MB)
- Fixed Dockerfile to pass "stdio" subcommand to entry point
- MCP protocol handshake verified with initialize request
- Protocol version 2024-11-05 confirmed
- Server name: rmcp, version 0.2.1
- Requires ES_URL environment variable (not ELASTICSEARCH_URL)
- NOTE: Server is deprecated, superseded by Elastic Agent Builder
- Tested with proper --name flag for container

docker-compose.yml

@@ -385,11 +385,11 @@ services:
     image: kneldevstack-aimiddleware-elasticsearch-mcp
     build:
       context: ./vendor/mcp-server-elasticsearch
-      dockerfile: Dockerfile
+      dockerfile: ../../dockerfiles/elasticsearch-mcp/Dockerfile
     container_name: kneldevstack-aimiddleware-elasticsearch-mcp
     restart: unless-stopped
     environment:
-      - ELASTICSEARCH_URL=${ELASTICSEARCH_URL:-http://localhost:9200}
+      - ES_URL=${ES_URL:-http://localhost:9200}
       - ELASTICSEARCH_USERNAME=${ELASTICSEARCH_USERNAME}
       - ELASTICSEARCH_PASSWORD=${ELASTICSEARCH_PASSWORD}
     ports: