MAINT-13 round 2: read the price gate without a new main.py option read

test_static_tariff forbids main.py reading `static_profile`; a small
static_gated() in static_tariff.py answers it, and the Controller keeps the
answer in `_price_gated` beside `cheap`.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Bdqr7PiaHcBnzPituu2yTC

goodwe_controller/app/static_tariff.py

@@ -1232,6 +1232,16 @@ def static_plan(opts: dict, since: datetime, until: datetime, *,
         profile, "fallback" if provisional else "static")
 
 
+def static_gated(opts: dict, now: datetime) -> bool:
+    """MAINT-13: is a fixed tariff set up, so that a cheap window can hold a
+    charge back? False for no profile or one that cannot be used."""
+    try:
+        return bool(static_plan(opts, now, now + timedelta(days=MEAN_WINDOW_DAYS),
+                                now=now).has_prices)
+    except ProfileInvalid:
+        return False
+
+
 def static_status(opts: dict, now: datetime):
     """(cheap, words) for the status page and for main.py's cheap-window flag.