feat(reset): config wipe, setup screen, and re-exec into provisioning (story 4-2)

Add _handle_reset() and _make_setup_screen() to main.py; integrate ButtonHoldDetector
and LEDController into the radar loop; LED lights immediately on hold, config is wiped,
setup screen shown, then os.execvp hands off to planemapper-provision. Wipe failures
log ERROR and abort without exec. Completes epic-4.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_reset.py

@@ -0,0 +1,48 @@
+from __future__ import annotations
+
+from unittest.mock import MagicMock, patch
+
+import pytest
+from gpiozero import Device
+from gpiozero.pins.mock import MockFactory
+from PIL import Image
+
+from planemapper.display import NullDisplay
+from planemapper.gpio_ctrl import LEDController
+from planemapper.main import _handle_reset
+
+
+@pytest.fixture(autouse=True)
+def mock_gpio():
+    Device.pin_factory = MockFactory()
+
+
+def test_reset_wipes_config_and_execvp():
+    display = NullDisplay()
+    led = LEDController()
+    with patch("planemapper.main.wipe_config") as mock_wipe:
+        with patch("planemapper.main.os.execvp") as mock_exec:
+            _handle_reset(display, led)
+            mock_wipe.assert_called_once()
+            mock_exec.assert_called_once_with("planemapper-provision", ["planemapper-provision"])
+
+
+def test_reset_shows_setup_screen():
+    display = MagicMock()
+    led = LEDController()
+    with patch("planemapper.main.wipe_config"):
+        with patch("planemapper.main.os.execvp"):
+            _handle_reset(display, led)
+            display.show.assert_called_once()
+            img = display.show.call_args[0][0]
+            assert isinstance(img, Image.Image)
+            assert img.size == (800, 480)
+
+
+def test_reset_does_not_execvp_on_wipe_failure():
+    display = NullDisplay()
+    led = LEDController()
+    with patch("planemapper.main.wipe_config", side_effect=PermissionError("no perms")):
+        with patch("planemapper.main.os.execvp") as mock_exec:
+            _handle_reset(display, led)
+            mock_exec.assert_not_called()