docs(discovery): precise wording on the watchdog, the empty state, recovery

Three comments this repair touches were still loose: "never rebuilt on a state
poll" (the discovery table, not the watchdog — the sensor's own poll does
refresh it when it has no fresh answer), and the class docstring's "recorded as
unknown" now says where a reader actually sees it, since the sensor reports
not_connected while the transport is down and unknown once it is up but the
sweep delivered nothing.

custom_components/nvidia_shield/sensor.py

@@ -168,8 +168,9 @@ class NvidiaShieldAppsSensor(NvidiaShieldSensorBase):
     runs once when the entity is added and then only when the table has gone
     stale: ``async_update`` goes through the manager's TTL cache, so a poll on a
     fresh table issues NO shell. A sweep that could not run is NOT an answer
-    (t62 F1): it is recorded as ``unknown`` and retried on the next update
-    instead of being frozen as a stamped-empty table for APP_LIST_TTL, while a
+    (t62 F1): it is recorded as ``unknown`` — or shown as ``not_connected``
+    while the transport itself is down — and retried on the next update instead
+    of being frozen as a stamped-empty table for APP_LIST_TTL, while a
     sweep that ran and found nothing IS the answer ``ok`` with a count of 0. On
     top of that the user can ask for a refresh with the standard
     ``homeassistant.update_entity`` action, and the Configure page runs the same