Add SG-Ready startup grace period and daily PV yield tracking

SG-Ready startup grace period (sg_ready_startup_min: 10):
Heat pump compressor takes ~9 minutes to start after receiving the
SG-Ready signal. Previously, idle detection fired after only 3×2min=6min,
turning off SG-Ready before the compressor had time to respond. The grace
period suppresses idle detection for the configured duration after activation.
0 = disabled (tests and unconfigured deployments are unaffected).

Daily PV yield (photovoltaic_production_cumulated_currentDay):
Reads actual kWh produced today from Prometheus (Wh → kWh, ÷1000).
Logged as pv_today_kwh each cycle. Shown on status page in two places:
- PV card sub-line: "Heute: 31.9 kWh"
- Forecast card alongside forecast: "Ist: 31.9 kWh"
Immediately makes forecast vs reality visible (today: forecast 15.9,
actual 31.9 kWh — explains why SOC bypass triggered).

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

internal/status/status.go

@@ -183,6 +183,7 @@ type pageData struct {
 	BatterySOC       float64
 	GridPowerW       float64
 	PVProductionW    float64
+	PVYieldTodayKWh  float64
 	AmbientTempC     float64
 	CompressorPowerW float64
 	WWTopTempC       float64
@@ -281,6 +282,7 @@ func (s *Store) Handler() http.HandlerFunc {
 			BatterySOC:       s.state.BatterySOC,
 			GridPowerW:       s.state.GridPowerW,
 			PVProductionW:    s.state.PVProductionW,
+			PVYieldTodayKWh:  s.state.PVYieldTodayKWh,
 			AmbientTempC:     s.state.AmbientTempC,
 			CompressorPowerW: s.state.CompressorPowerW,
 			WWTopTempC:       s.state.WWTopTempC,
@@ -833,6 +835,7 @@ h1 { font-size: 1.4rem; font-weight: 700; color: #14532d; }
   <div class="card">
     <div class="card-label">PV-Leistung</div>
     <div class="card-value" style="color:#d97706">{{formatW .PVProductionW}}</div>
+    {{if gt .PVYieldTodayKWh 0.0}}<div class="card-sub">Heute: {{printf "%.1f" .PVYieldTodayKWh}} kWh</div>{{end}}
   </div>
 
   <!-- Temperature -->
@@ -865,6 +868,7 @@ h1 { font-size: 1.4rem; font-weight: 700; color: #14532d; }
     <div class="forecast-row">
       <span class="forecast-icon">{{.Forecast.Icon}}</span>
       <span class="card-value" style="color:#d97706">{{printf "%.1f" .Forecast.KWh}} kWh</span>
+      {{if gt .PVYieldTodayKWh 0.0}}<span class="card-sub" style="margin-left:1rem">Ist: {{printf "%.1f" .PVYieldTodayKWh}} kWh</span>{{end}}
     </div>
     <div class="forecast-quality">{{.Forecast.Quality}}</div>
   </div>