fix(setup): register scaffolded target with ProcessorManager + final-review hardening

Final-review blocker: the setup scaffold created the LED output target in the
store but never registered it with the ProcessorManager, so the wizard's
"Start" step 404'd on a fresh setup (target not found) — the lights never
started despite a success screen. Now the scaffold calls
target.register_with_manager(manager) right after create (mirroring the
canonical POST /output-targets route, same ValueError guard), so
start_processing finds the target. Rollback unregisters via
manager.remove_target before deleting the store entity, so a post-registration
failure leaves no half-registered target.

Also from the final review:
- solve corner_indices elements now bounded ge=0 (clear 422 instead of silent
  modulo-wrap).
- setup-wizard.ts: reuse tutorials' suppressGettingStartedTour()/TOUR_KEY
  instead of a duplicated 'tour_completed' literal; drop a duplicate manual-form
  submit listener.

Tests: + adversarial pass over the whole feature (solver/session/scaffold edge
cases) and a scaffold->register->startable regression test. Full suite
2149 passed / 2 skipped; tsc clean; build passes; ruff clean.

server/tests/api/routes/test_setup_routes.py

@@ -21,7 +21,7 @@ from __future__ import annotations
 import pytest
 from fastapi import FastAPI
 from fastapi.testclient import TestClient
-from unittest.mock import patch
+from unittest.mock import MagicMock, patch
 
 
 # ---------------------------------------------------------------------------
@@ -89,6 +89,14 @@ def event_log():
     return log
 
 
+@pytest.fixture
+def mock_manager():
+    """A MagicMock ProcessorManager that silently accepts all calls."""
+    mgr = MagicMock()
+    mgr.remove_target = MagicMock()
+    return mgr
+
+
 @pytest.fixture
 def setup_client(
     tmp_db,
@@ -98,6 +106,7 @@ def setup_client(
     css_store,
     output_target_store,
     event_log,
+    mock_manager,
 ):
     from ledgrab.api.routes.setup import router
     from ledgrab.api.auth import verify_api_key
@@ -111,6 +120,7 @@ def setup_client(
     app.dependency_overrides[deps.get_picture_source_store] = lambda: picture_source_store
     app.dependency_overrides[deps.get_color_strip_store] = lambda: css_store
     app.dependency_overrides[deps.get_output_target_store] = lambda: output_target_store
+    app.dependency_overrides[deps.get_processor_manager] = lambda: mock_manager
 
     # Capture entity events
     def _fire(entity_type, action, entity_id):
@@ -512,3 +522,79 @@ class TestScaffoldCalibrationIntegration:
         assert updated.calibration.leds_top == 15
         assert updated.calibration.leds_right == 9
         assert updated.calibration.layout == "clockwise"
+
+
+# ---------------------------------------------------------------------------
+# Regression: scaffold registers the output target with ProcessorManager
+# ---------------------------------------------------------------------------
+
+
+class TestScaffoldRegistersWithManager:
+    def test_scaffold_calls_add_target_on_manager(
+        self,
+        setup_client,
+        sample_device,
+        mock_manager,
+    ):
+        """Blocker regression: scaffold must register the created output target
+        with the ProcessorManager so that a subsequent start call can find it.
+
+        WledOutputTarget.register_with_manager calls manager.add_target(...)
+        — we assert that method was invoked with the scaffolded target id.
+        """
+        resp = _scaffold(setup_client, device_id=sample_device.id)
+        assert resp.status_code == 201, resp.text
+        target_id = resp.json()["output_target_id"]
+
+        # register_with_manager → manager.add_target(target_id=..., ...)
+        mock_manager.add_target.assert_called_once()
+        call_kwargs = mock_manager.add_target.call_args
+        assert call_kwargs.kwargs.get("target_id") == target_id, (
+            f"manager.add_target was not called with target_id={target_id!r}; "
+            f"actual call: {call_kwargs}"
+        )
+
+    def test_scaffold_rollback_calls_remove_target_on_manager(
+        self,
+        setup_client,
+        sample_device,
+        output_target_store,
+        mock_manager,
+    ):
+        """Rollback after a post-target-creation failure must call manager.remove_target
+        so no half-registered target lingers in the ProcessorManager.
+
+        We inject a failure by making register_with_manager raise RuntimeError
+        (bypassing the ValueError-only guard), which puts the outer except branch
+        in play.  The target IS already in created_ids at that point, so rollback
+        must call manager.remove_target(target_id).
+        """
+        created_target_ids: list[str] = []
+
+        original_create = output_target_store.create_wled_target
+
+        def _spy_create(*args, **kwargs):
+            target = original_create(*args, **kwargs)
+            created_target_ids.append(target.id)
+            return target
+
+        output_target_store.create_wled_target = _spy_create
+        try:
+            # Patch register_with_manager on WledOutputTarget to raise RuntimeError —
+            # RuntimeError bypasses the ValueError guard and triggers the outer except,
+            # so rollback fires with the target already in created_ids.
+            with patch(
+                "ledgrab.storage.wled_output_target.WledOutputTarget.register_with_manager",
+                side_effect=RuntimeError("Injected registration failure for rollback test"),
+            ):
+                resp = setup_client.post(
+                    "/api/v1/setup/scaffold",
+                    json={"device_id": sample_device.id, "display_index": 0},
+                )
+            assert resp.status_code == 500, resp.text
+
+            assert len(created_target_ids) == 1, "spy did not record a created target"
+            target_id = created_target_ids[0]
+            mock_manager.remove_target.assert_called_with(target_id)
+        finally:
+            output_target_store.create_wled_target = original_create