Implement unit tests for MCP server

[bhf]

As identified in #147, the MCP server (src/mcp-server.ts) currently lacks automated unit tests to verify tool definitions and request handlers.

Goal

Implement unit tests for the MCP server to ensure:

• Tool registration is correct.
• Resource listing/retrieval handlers correctly interface with the K8s library.
• Error handling (e.g., K8s API failures) returns appropriate MCP error responses.

Scope

• Use Vitest and the MCP SDK's testing utilities or mock StdioServerTransport to trigger and validate tool calls.
• Mock src/lib/k8s.ts functions to decouple from actual Kubernetes API logic.

Acceptance Criteria

• Create src/__tests__/mcp-server.test.ts.
• Test the list_tools handler.
• Test call handlers for at least 3 core tools (e.g., list_pods, get_pod_logs).
• Validate error handling when the underlying K8s library throws.