feat(orchestrator): MVP synthetic life-injection worker (SSH only)

Adds a new decnet orchestrate worker whose job is to keep the honeypot
ecosystem from looking suspiciously static — a frozen LAN with no
inter-host traffic and no filesystem aging is its own honeypot tell.

MVP scope:
- New OrchestratorEvent table + repo methods (purpose-built sibling
  to Log so synthetic events stay separable from attacker-driven ones).
- New orchestrator.{activity,file}.<decky_id> bus topics +
  system.orchestrator.health heartbeat.
- SSH-only driver. Traffic action runs python3 inside src container
  to TCP-connect dst:22 and read the SSH banner — real on-the-wire
  SSH-protocol traffic without shipping creds. File action drops or
  refreshes a small file via docker exec on the destination.
- Random scheduler (50/50 traffic/file when >=2 SSH-capable deckies
  are running). Diurnal shaping, role-aware pairing, and session-aware
  backoff are explicit non-goals for MVP.
- CLI registration, systemd unit (SupplementaryGroups=docker),
  worker-registry entry so the dashboard shows orchestrator health.
- 11 tests: scheduler policy, driver argv shape + injection-safety,
  end-to-end one-tick integration with FakeBus + SQLite.

decnet/orchestrator/drivers/base.py

@@ -0,0 +1,27 @@
+"""Driver protocol for orchestrator actions.
+
+Future protocols (HTTP, SMB, MySQL, …) implement this interface alongside
+the SSH driver. Kept deliberately minimal — the orchestrator only needs
+"run this action and tell me how it went".
+"""
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import Any, Protocol
+
+from decnet.orchestrator.scheduler import Action
+
+
+@dataclass
+class ActivityResult:
+    """Outcome of one driver invocation.
+
+    ``payload`` is the per-action JSON envelope the worker writes to the
+    ``OrchestratorEvent.payload`` column and to the bus event body.
+    """
+    success: bool
+    payload: dict[str, Any] = field(default_factory=dict)
+
+
+class Driver(Protocol):
+    async def run(self, action: Action) -> ActivityResult: ...