feat: add NATS/JetStream mode for MCP tool requests and receipts

[rodaddy]

Goal

Make mcp2cli a first-class NATS/JetStream citizen for tasking, progress, receipts, and remote tool invocation.

Motivation

Rico's agent workflows already use NATS/JetStream concepts for assignment, progress, completion, receipts, and k-board updates. mcp2cli should be able to sit on the event bus as a durable MCP hub instead of requiring every agent to run random local MCP processes.

Proposed capabilities

• Subscribe to request subjects such as mcp2cli.request.<service>.<tool>.
• Publish replies to NATS request/reply or explicit reply subjects.
• Emit lifecycle events:
  • mcp2cli.tool.started
  • mcp2cli.tool.completed
  • mcp2cli.tool.failed
  • mcp2cli.service.connected
  • mcp2cli.service.unhealthy
  • mcp2cli.schema.changed
• JetStream persistence for receipts and replayable audit trails.
• Correlation IDs for k-board/OB/Discord receipts.
• Subject-level allow/block policy per service/tool.
• Optional queue groups for horizontal workers.

Example

mcp2cli nats serve --config /etc/mcp2cli/services.json --subject-prefix mcp2cli
mcp2cli nats call open-brain session_context --params '{"session_key":"overlay-vnext"}'

Acceptance criteria

• A NATS request can invoke an MCP tool and receive structured JSON.
• Tool execution emits progress/completion/failure events with correlation IDs.
• Failures are agent-friendly and secret-safe.
• NATS mode works with the same service registry and policies as CLI/HTTP daemon mode.
• Receipts can be consumed by PG k-board/Open Brain workflows.