UX-13 P0 review: keep unread keys, back off a failed entity read

- uimodel: editing a listed inverter keeps the stored flat keys, and a
  region of "own" keeps a stored price_taxes_profile (both were dropped).
- haentities: a failed read also waits CACHE_S, so polls while Home
  Assistant is down do not queue one 10 s read each.
- ui_text: the Flanders preset names its DSO, and the help says
  Wallonia and Brussels have no figures yet. REGION_PRESETS cites the card.
- tests: decode of a reversed solar row, both kept keys, the backoff.

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

goodwe_controller/app/haentities.py

@@ -51,13 +51,17 @@ class EntityCache:
         self.clock = clock
         self.rows: dict | None = None
         self.read_at: float | None = None
+        self.tried_at: float | None = None
         self._lock = asyncio.Lock()
 
     async def get(self) -> tuple[dict | None, float | None]:
         """(rows by entity id, age in s), or (None, None) if never read."""
         async with self._lock:      # one HA read however many pickers ask
             now = self.clock()
-            if self.read_at is None or now - self.read_at >= CACHE_S:
+            # A failed read also waits CACHE_S, so polls while HA is down do
+            # not queue one 10 s read each behind this lock.
+            if self.tried_at is None or now - self.tried_at >= CACHE_S:
+                self.tried_at = now
                 states = await self.hass.states()
                 if states is not None:
                     rows = (row(s) for s in states)