feat(coordination): wire real executor to coordination_orchestrate MCP tool

## Current state

`coordination_orchestrate` (in `src/mcp-tools/coordination-tools.ts`) currently records an orchestration request in the coordination store but does not execute it. The response includes:

```json
{
"executor": "none",
"_note": "coordination_orchestrate currently records the orchestration request but does not execute it. For real multi-agent execution use agent_spawn + the Task tool, or hive-mind_spawn for queen-led coordination."
}
```

This is intentionally honest (ADR-093 F7) — the previous implementation returned a hardcoded `estimatedCompletion: "50ms"` which was misleading.

## What needs to happen

Wire a real executor so callers can use `coordination_orchestrate` to actually dispatch work, not just schedule a record. The executor should:
- Accept a task + agent list + strategy
- Dispatch via the agent pool or hive-mind
- Return real status updates

## Alternatives

The `_note` already points callers to `agent_spawn` + Task tool + `hive-mind_spawn`. If those cover all use cases, this tool could alternatively be formally deprecated with a clear deprecation message.

## Tracking

Found during quality sweep (issue #2138, territory T5 — mocked/placeholder claims).

Start in src/mcp-tools/coordination-tools.ts and trace how coordination_orchestrate records requests and produces its current response. Read the existing agent_spawn, Task tool, and hive-mind_spawn entry points to compare dispatch options. Done means the tool either dispatches the task through a real executor and returns status updates, or is formally deprecated with a clear message.

Written by the indexing model from the issue text.