Make mcp-kubernetes stdio-only and remove remote deployment support

## Breaking change

The next major release will support only the MCP stdio transport. SSE and streamable HTTP transports, container-image distribution, and Kubernetes/Helm deployment artifacts will be removed.

## Rationale

This project is a local MCP server. It executes local command-line tools using the identity of the MCP process, and it is not intended to expose those tools as a remote service.

## Scope

- Remove SSE and streamable HTTP runtime support.
- Remove HTTP-only authentication, token forwarding, and network configuration.
- Remove Helm/Kubernetes deployment artifacts and documentation.
- Stop building, publishing, signing, and attesting container images and Helm charts.
- Retain local stdio execution and binary releases.

## Migration

Install the released binary locally and configure your MCP client to start it as a stdio subprocess. Remote deployments must not be upgraded in place; move the client configuration to a local stdio installation instead.

## Out of scope

This change does not remove the optional Helm MCP tool. That capability will be evaluated separately.

The issue names no files or tests. Start by mapping the runtime transports, authentication and network configuration, Kubernetes/Helm artifacts, and release workflows; confirm how local stdio execution and binary releases are retained. Done means remote support and deployment artifacts are removed while local stdio installation remains documented.

Written by the indexing model from the issue text.