feat(ml): lease announces detector config; agent builds proposers from it live (#134 step 2)

The GPU lease now carries the crop-proposer config from MLSettings in a per-job
'detectors' block (same pattern as embed_model_name). The agent's worker builds
its Proposers from the announced config via _effective_cfg (lease block overlaid
on env) + _proposers_for (rebuilds only when a config signature changes) — so an
operator's UI edit takes effect on the next lease with NO restart, and env is now
just the bootstrap fallback until the server announces. enabled-off maps to empty
weights (proposer skipped); dedupe_iou + max_regions also come from the effective
cfg. Test: lease announces the detectors block with the seeded default weights.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CDgx8bQS5YrGRK76v8HUnM

backend/app/api/gpu.py

@@ -269,6 +269,33 @@ async def lease():
             ).scalars()
         } if ids else {}
         await session.commit()
+        # Crop-proposer config, announced FROM THE SETTING like embed_model_name
+        # (#134): the agent builds its detectors from this, rebuilding live when
+        # it changes — so tuning is a DB/UI edit, never an agent restart. Same
+        # block for every job in the batch (it's global), built once. An enabled
+        # toggle off is carried through so the agent skips that proposer.
+        detectors = {
+            "person": {
+                "enabled": ml.detector_person_enabled,
+                "weights": ml.detector_person_weights,
+                "conf": ml.detector_person_conf,
+            },
+            "anatomy": {
+                "enabled": ml.detector_anatomy_enabled,
+                "weights": ml.detector_anatomy_weights,
+                "conf": ml.detector_anatomy_conf,
+            },
+            "panel": {
+                "enabled": ml.detector_panel_enabled,
+                "weights": ml.detector_panel_weights,
+                "conf": ml.detector_panel_conf,
+            },
+            "max_figures": ml.detector_max_figures,
+            "max_components": ml.detector_max_components,
+            "max_panels": ml.detector_max_panels,
+            "max_regions": ml.detector_max_regions,
+            "dedupe_iou": ml.detector_dedupe_iou,
+        }
         out = []
         for j in jobs:
             img = imgs.get(j.image_record_id)
@@ -290,6 +317,7 @@ async def lease():
                 # re-embed, never an agent change.
                 "embed_model_name": ml.embedder_model_name,
                 "embed_version": ml.embedder_model_version,
+                "detectors": detectors,
             })
     return jsonify({"jobs": out})