Hands: fix Export doing nothing, and show it's busy at once

af2ea7c put _stay_awake between exportSession and its @Slot, so the
window's Export button called a method QML couldn't see. A new test checks
every backend call in main.qml against Backend's slots and properties.
Export and Upload now say Exporting…/Uploading… with a spinner the moment
they're pressed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

hands/rec/tests/test_qml_backend.py

@@ -0,0 +1,43 @@
+#!/usr/bin/env python3
+"""main.qml against ft_handrec.Backend: every backend.name(...) the window calls is a slot, and
+every backend.name it reads is a property or a slot. A method that lost its @Slot shows up in
+QML only as "is not a function" when its button is pressed (2026-10-03: Export did nothing).
+Needs PySide6 (the dev container); skipped without it.
+
+  python3 hands/rec/tests/test_qml_backend.py
+"""
+import os
+import re
+import sys
+import unittest
+
+HERE = os.path.dirname(os.path.abspath(__file__))
+REC = os.path.dirname(HERE)
+sys.path.insert(0, REC)
+
+
+class QmlBackendTest(unittest.TestCase):
+    def setUp(self):
+        try:
+            import ft_handrec
+        except ImportError as e:
+            self.skipTest(f"no PySide6: {e}")
+        meta = ft_handrec.Backend.staticMetaObject
+        self.slots = {bytes(meta.method(i).name()).decode() for i in range(meta.methodCount())}
+        self.props = {meta.property(i).name() for i in range(meta.propertyCount())}
+        with open(os.path.join(REC, "main.qml")) as f:
+            self.qml = f.read()
+
+    def test_calls_are_slots(self):
+        called = set(re.findall(r"\bbackend\.(\w+)\s*\(", self.qml))
+        self.assertTrue(called)
+        self.assertEqual(sorted(called - self.slots), [], "called from main.qml but not a slot")
+
+    def test_reads_exist(self):
+        read = set(re.findall(r"\bbackend\.(\w+)\b(?!\s*\()", self.qml))
+        self.assertTrue(read)
+        self.assertEqual(sorted(read - self.props - self.slots), [], "read in main.qml but not on Backend")
+
+
+if __name__ == "__main__":
+    unittest.main()