Add go-e wallbox charger integration

- charger.go: polls go-e /api/status?filter=nrg,eto every 10 s
- db.go: WriteCharger() inserts into charger hypertable
- config.go: ChargerConf with host field
- main.go: polls charger in parallel with inverter and meters
- schema.sql: charger table + charger_10m/1h/daily aggregates + policies

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

schema.sql

@@ -98,10 +98,40 @@ SELECT time_bucket('1 day', time) AS bucket,
 FROM power_meter
 GROUP BY bucket, device;
 
+-- Written by energy-collector every 10 s
+CREATE TABLE charger (
+    time    TIMESTAMPTZ NOT NULL,
+    power   REAL,    -- W total charging power
+    eto_wh  BIGINT   -- Wh cumulative total energy (from go-e eto field)
+);
+SELECT create_hypertable('charger', 'time', chunk_time_interval => INTERVAL '7 days');
+
+CREATE MATERIALIZED VIEW charger_10m
+WITH (timescaledb.continuous, timescaledb.materialized_only = false) AS
+SELECT time_bucket('10 minutes', time) AS bucket,
+       AVG(power)                      AS power
+FROM charger
+GROUP BY bucket;
+
+CREATE MATERIALIZED VIEW charger_1h
+WITH (timescaledb.continuous, timescaledb.materialized_only = false) AS
+SELECT time_bucket('1 hour', bucket) AS bucket,
+       AVG(power)                    AS power
+FROM charger_10m
+GROUP BY 1;
+
+CREATE MATERIALIZED VIEW charger_daily
+WITH (timescaledb.continuous, timescaledb.materialized_only = false) AS
+SELECT time_bucket('1 day', time) AS bucket,
+       last(eto_wh, time)         AS eto_wh
+FROM charger
+GROUP BY bucket;
+
 -- ── Retention — keep 30 days of raw data; aggregates stay forever ─────────────
 
 SELECT add_retention_policy('inverter',    INTERVAL '30 days');
 SELECT add_retention_policy('power_meter', INTERVAL '30 days');
+SELECT add_retention_policy('charger',     INTERVAL '30 days');
 
 -- ── Refresh policies ──────────────────────────────────────────────────────────
 
@@ -135,6 +165,22 @@ SELECT add_continuous_aggregate_policy('power_meter_daily',
     end_offset        => INTERVAL '1 day',
     schedule_interval => INTERVAL '1 day');
 
--- Grant SELECT on all tables and views (including continuous aggregates) to energy.
--- Run after all views are created so the grant covers them.
+SELECT add_continuous_aggregate_policy('charger_10m',
+    start_offset      => INTERVAL '1 hour',
+    end_offset        => INTERVAL '10 minutes',
+    schedule_interval => INTERVAL '10 minutes');
+
+SELECT add_continuous_aggregate_policy('charger_1h',
+    start_offset      => INTERVAL '3 hours',
+    end_offset        => INTERVAL '1 hour',
+    schedule_interval => INTERVAL '1 hour');
+
+SELECT add_continuous_aggregate_policy('charger_daily',
+    start_offset      => INTERVAL '3 days',
+    end_offset        => INTERVAL '1 day',
+    schedule_interval => INTERVAL '1 day');
+
+-- Grant privileges after all objects are created.
+-- INSERT on raw hypertables (collector writes), SELECT on everything else (frontend reads).
+GRANT INSERT ON inverter, power_meter, charger TO energy;
 GRANT SELECT ON ALL TABLES IN SCHEMA public TO energy;