fix: advance dream cursor when Dream is disabled to prevent prompt bloat (#4242)

When dream.enabled is false, the Dream cron job never runs, so the
dream cursor (.dream_cursor) stays at its initial value (0). This
causes read_recent_history_for_prompt() to treat every history entry
as unprocessed, injecting the full chat history into every system
prompt and growing without bound.

Fix: fast-forward the dream cursor to the latest history entry at
gateway startup when Dream is disabled.

nanobot/cli/commands.py

@@ -1165,6 +1165,7 @@ def _run_gateway(
         console.print(f"[green]✓[/green] Dream: {dream_cfg.describe_schedule()}")
     else:
         console.print("[yellow]○[/yellow] Dream: disabled")
+        agent.context.memory.set_last_dream_cursor(agent.context.memory.get_latest_cursor())
 
     # Register Heartbeat system job (idempotent on restart)
     if hb_cfg.enabled: