PRICE-01: price_service provider, fallback chain, and the gate read from it

A new price source, `price_provider: price_service`: the owner's price server,
one fixed HTTPS host, a bearer token (new password option
`price_service_token`), wholesale energy only so markup and taxes are added as
for generic_dayahead.

The chain is server, then energy-charts, then the prices the history store
kept. A step counts only if it has a price for now. Each step down and back up
is one log line. With every source down a site plans from what it saved.

No price for now: one status row, one Home plan line and one notification, in
English and Dutch, cleared when a price returns. With this provider the
maintenance charge gate reads the provider's prices and keeps the Home
Assistant rule: the current 15-minute price is at or below today's average.

The token is hidden on the settings page, refused when missing, and taken out
of any error text. Other providers, `off` and the Home Assistant pair take the
road they always took (scripted-day probe against 0ce7d35: one line differs,
the refusal that lists the known providers). See
DECISIONS/PRICE-01-own-price-server.md.

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

goodwe_controller/test_arbitrage.py

@@ -81,6 +81,7 @@ from datetime import datetime, timedelta, timezone
 from app import arbitrage as _arb
 from named_absence import first
 from app import main as _main
+from app.price_chain import PriceWatch
 from app import peakguard as _pg
 from app.arbiter import (
     P_ARBITRAGE, P_LOOP, P_MAINT_SHAPE, P_MAINTENANCE, P_PEAK, P_SAFETY, Claim,
@@ -2311,6 +2312,7 @@ class _T12Controller:
         self.tariff_plan = None
         self.tariff_at = None
         self.price_history = NoHistory()
+        self.price_watch = PriceWatch()      # PRICE-01: the refresh passes it on
         self.stop_event = asyncio.Event()
         self.stop_event.set()          # so the inter-refresh wait returns
         self._ticks = 0