feat(agent): autoscale the worker count (throughput hill-climb), Auto default-on

The new per-job workload (3 detectors + several SigLIP embeds) is far more
GPU-bound than the old I/O-bound CCIP pass, so the right worker count shifted and
is hard to guess. Add an Auto mode (default ON) that finds it:

- _control_loop samples jobs/sec + GPU util/VRAM every ~6s and hill-climbs the
  target: grow while throughput keeps improving and VRAM stays under budget,
  revert a step that doesn't help, back off under memory pressure (VRAM >= 90%),
  then settle and periodically re-probe (the GPU/IO balance shifts over a run).
- A manual concurrency set is an override → leaves Auto; an "Auto" toggle in the
  control UI re-enables it. status() reports `auto`; the dial reflects the
  auto-chosen count (read-only) while Auto is on.
- AUTO_SCALE env (default on) + compose doc. Agent py-compiled (outside CI).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ttrj5P7upUTueSfoJcxEqa

agent/docker-compose.yml

@@ -34,6 +34,10 @@ services:
       # Resume the worker automatically on container start (survive a reboot /
       # crash-restart while you're away). Set to 0 to require a manual Start.
       AUTO_START: ${AUTO_START:-1}
+      # Autoscale the worker count (throughput hill-climb that finds the sweet
+      # spot + backs off under VRAM pressure). On by default; toggle live in the
+      # control UI. Set to 0 to start in manual mode.
+      AUTO_SCALE: ${AUTO_SCALE:-1}
       # Crop embedder (SigLIP concept bag): float16 keeps VRAM low on a shared
       # desktop GPU; the model itself is announced by the server.
       SIGLIP_DTYPE: ${SIGLIP_DTYPE:-float16}