fix: flake8 E701 in avatar handler; update SSH test to match accept-new

- app.py: split 'with open(sentinel): pass' onto two lines (flake8 E701)
- tests/test_diagnose.py: rename test and assert StrictHostKeyChecking=accept-new (not =no which was fixed earlier)

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

app.py

@@ -594,7 +594,8 @@ def api_avatar():
                 pass
 
     if not avatar_data or len(avatar_data) < 100:
-        with open(sentinel, 'w'): pass
+        with open(sentinel, 'w'):
+            pass
         return '', 404
 
     # Validate JPEG magic bytes (FF D8 FF)

tests/test_diagnose.py

@@ -9,9 +9,9 @@ from diagnose import DiagnosticsRunner  # noqa: E402
 # ── build_ssh_command ────────────────────────────────────────────────────────
 
 class TestBuildSshCommand:
-    def test_contains_stricthostkeychecking_no(self):
+    def test_contains_stricthostkeychecking_accept_new(self):
         cmd = DiagnosticsRunner.build_ssh_command('10.0.0.1', 'eth0')
-        assert 'StrictHostKeyChecking=no' in cmd
+        assert 'StrictHostKeyChecking=accept-new' in cmd
 
     def test_contains_host_ip(self):
         cmd = DiagnosticsRunner.build_ssh_command('10.0.0.1', 'eth0')