Make daily traffic scale to dozens of screens: incremental sync, ping keepalive, one action per message (0.2.39)

App 0.2.39 / firmware 0.2.33, items 1, 2, 4, 5 and 6 of the 30-screen scaling check.

- Only the tiles (and top bar) of changed entities are rebuilt; the screen list is
  cached until the registry or a screen diagnostic changes; the SSE stream follows.
- Sensor history comes from one recorder/statistics_during_period call per window in
  a background task, with the REST history as fallback per sensor without statistics.
- Firmware 0.2.33 answers a keepalive ping with its layout revision; a mismatch or a
  restart asks for the layout again, everything is repeated hourly as a safety net.
- The screen_message API action takes one whole message; the text inbox chunks stay
  as fallback for older firmware. A repeated unchanged layout keeps the inbox state.
- Quiet diagnostics: Opgestart (uptime as timestamp) replaces Uptime, heap every
  5 min, setting numbers publish only on change.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

tests/test_header_bar.py

@@ -244,7 +244,7 @@ class ManagerTests(unittest.IsolatedAsyncioTestCase):
                 self.states = {'text.screen': state('Ready'), 'sensor.fw': state(firmware), 'light.a': state('on'),
                                'sensor.t': state('21.34', unit_of_measurement='°C', device_class='temperature'),
                                'binary_sensor.deur': state('off', device_class='door')}
-            async def send(self, inbox, message):
+            async def send(self, inbox, message, action=None):
                 self.messages.append(message)
         return Manager(HA(), path)