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- NOTE: Server is deprecated, superseded by Elastic Agent Builder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

dockerfiles/elasticsearch-mcp/Dockerfile

@@ -0,0 +1,28 @@
+# Copyright Elasticsearch B.V. and contributors
+# SPDX-License-Identifier: Apache-2.0
+
+FROM rust:1.89@sha256:c50cd6e20c46b0b36730b5eb27289744e4bb8f32abc90d8c64ca09decf4f55ba AS builder
+
+WORKDIR /app
+
+COPY Cargo.toml Cargo.lock ./
+
+# Cache dependencies
+RUN mkdir -p ./src/bin && \
+    echo "pub fn main() {}" > ./src/bin/elasticsearch-core-mcp-server.rs && \
+    cargo build --release
+
+COPY src ./src/
+
+RUN cargo build --release
+
+#--------------------------------------------------------------------------------------------------
+
+FROM cgr.dev/chainguard/wolfi-base:latest
+
+COPY --from=builder /app/target/release/elasticsearch-core-mcp-server /usr/local/bin/elasticsearch-core-mcp-server
+
+ENV CONTAINER_MODE=true
+
+EXPOSE 8080/tcp
+ENTRYPOINT ["/usr/local/bin/elasticsearch-core-mcp-server", "stdio"]