Implement story 1.5: provisioning execution tile download cache validation wifi kill

Add tiles.py, airspace.py, wifi.join_home_wifi, portal /submit route, and rewire
provision.py main loop; all tasks and quality gates pass (56 tests, ruff clean).

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

tests/provisioning/test_wifi.py

@@ -0,0 +1,22 @@
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from planemapper.provisioning import ProvisioningError
+from planemapper.provisioning.wifi import join_home_wifi
+
+
+def test_join_home_wifi_success() -> None:
+    mock_result = MagicMock()
+    mock_result.returncode = 0
+    with patch("planemapper.provisioning.wifi.subprocess.run", return_value=mock_result):
+        join_home_wifi("MySSID", "MyPass")
+
+
+def test_join_home_wifi_failure() -> None:
+    mock_result = MagicMock()
+    mock_result.returncode = 1
+    mock_result.stderr = b"Error: connection failed"
+    with patch("planemapper.provisioning.wifi.subprocess.run", return_value=mock_result):
+        with pytest.raises(ProvisioningError, match="nmcli failed"):
+            join_home_wifi("MySSID", "wrongpassword")