OPT-17: the solar forecast can come from several entities, summed

New list options pv_forecast_entities and pv_forecast_tomorrow_entities
(same shape as pv_entities); the single-entity keys are unchanged.

- Each member is read in its own unit (Wh/kWh/MWh) in one gather and the
  day is summed. Hourly splits are merged when every member has one, else
  the total goes on the bell.
- A member missing, unavailable, stale, non-energy or bad makes that
  day's forecast unusable (no partial sum). A caution row names it by
  position; the action log names the entity once per change.
- Single key and list both set for one day: refused at start.
- A one-member list behaves exactly like the single key (test_opt17.py);
  the single-key path is byte-identical to e36565f over 24 scenarios.
- Supervisor shape measured: tools/supervisor_shape_probe.py section J.

DECISIONS/OPT-17-several-forecast-entities.md has the rules.

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

goodwe_controller/test_modes_p4.py

@@ -113,19 +113,21 @@ check("the harness bites: Leftover solar grid-charging with no plan moves "
              lambda: setattr(modetrade, "GRID_CHARGE_MODES",
                              (packmode.LEFTOVER_SOLAR, packmode.CHEAP_HOURS)),
              lambda: setattr(modetrade, "GRID_CHARGE_MODES", _gcm)))
-_read = solarfc.read
+# OPT-17: the controller reads through `read_sum()`, so that is the seam.
+_read = solarfc.read_sum
 
 
 def _as_dark(today, tomorrow, now, **kw):
-    return _read({"state": "0", "attributes": {"unit_of_measurement":
-                                               "kWh"},
-                  "last_updated": now.isoformat()}, None, now)
+    return _read([("sensor.f", {"state": "0", "attributes": {
+        "unit_of_measurement": "kWh"}, "last_updated": now.isoformat()})],
+        [], now)
 
 
 check("...and an unavailable forecast read as a dark one moves "
       "n2_sf_ls_fc_down (Leftover solar would buy its shortfall)",
-      _moved("n2_sf_ls_fc_down", lambda: setattr(solarfc, "read", _as_dark),
-             lambda: setattr(solarfc, "read", _read)))
+      _moved("n2_sf_ls_fc_down",
+             lambda: setattr(solarfc, "read_sum", _as_dark),
+             lambda: setattr(solarfc, "read_sum", _read)))
 
 # ============================================================================ #
 print("2. the forecast sensors")