fix: pace inter-tier polling; fix stale package-rename references in docs

mqtt_demo/samples/__init__.py

@@ -1,13 +1,13 @@
 """Appliance descriptors registry.
 
 Adding a new appliance class:
-  1. Write `appliances/<class>.py` with an ApplianceDescriptor named
-     after the class (uppercase, e.g. OVEN).
+  1. Write `mqtt_demo/samples/<class>.py` with an ApplianceDescriptor
+     named after the class (uppercase, e.g. OVEN).
   2. Add it to DESCRIPTORS below.
   3. Set DEVICE_CLASS=<class> in the per-device .env.
 
-main.py imports get_descriptor(name) to look up the descriptor at
-startup; the bridge itself stays class-agnostic.
+mqtt_demo/__main__.py imports get_descriptor(name) to look up the
+descriptor at startup; the bridge itself stays class-agnostic.
 """
 from ..descriptor import ApplianceDescriptor
 from .dryer import DRYER