Add a built-in Anker Solix V1 Smart EV Charger plugin

A Go re-implementation of the auth and read-only data flow from
thomluther/anker-solix-api, scoped to the V1 Smart EV Charger (A5191)
and adapted to DriverVault's plugin contract.

Login is a custom ECDH (P-256) + AES-256-CBC password exchange against
passport/login, yielding a ~7-day auth token plus gtoken = md5(user_id)
for subsequent requests; a fresh login covers expiry and 401/403. The
country code routes to the EU or global Anker server.

Exposes read-only capabilities (chargers, charger-status, charge-stats,
charge-orders, ocpp-info, devices, sites, vehicles) with a health check
that reports the bound-charger count.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

API Server/internal/plugins/builtin/builtin.go

@@ -12,6 +12,8 @@
 package builtin
 
 import (
+	// anker-solix — Anker Solix V1 Smart EV Charger read-only cloud data.
+	_ "drivervault/apiserver/internal/plugins/builtin/ankersolix"
 	// toyota — Toyota Connected Europe (MyToyota) read-only vehicle data.
 	_ "drivervault/apiserver/internal/plugins/builtin/toyota"
 )