feat: solar KPIs, version display, feature flags (v1.4.0)

New dashboard KPI cards:
- Performance Ratio (PR) with color thresholds
- Equivalent Utilization Hours
- Daily Revenue (¥)
- Self-Consumption Rate

Version display for field engineers:
- Login page footer: "v1.4.0 | Core: v1.4.0"
- Sidebar footer: version when expanded
- System Settings: full version breakdown

Backend (core sync):
- GET /api/v1/version (no auth) — reads VERSIONS.json
- GET /api/v1/kpi/solar — PR, revenue, equiv hours calculations
- Dashboard energy_today fallback from raw energy_data
- PV device filter includes sungrow_inverter type

Feature flags:
- Sidebar hides disabled features (charging, bigscreen_3d)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/layouts/MainLayout.tsx

@@ -12,7 +12,7 @@ import {
 import { Outlet, useNavigate, useLocation } from 'react-router-dom';
 import { useTranslation } from 'react-i18next';
 import { getUser, removeToken } from '../utils/auth';
-import { getAlarmStats, getAlarmEvents, getBranding } from '../services/api';
+import { getAlarmStats, getAlarmEvents, getBranding, getVersion } from '../services/api';
 import { useTheme } from '../contexts/ThemeContext';
 
 const { Header, Sider, Content } = Layout;
@@ -29,6 +29,7 @@ export default function MainLayout() {
   const [alarmCount, setAlarmCount] = useState(0);
   const [recentAlarms, setRecentAlarms] = useState<any[]>([]);
   const [features, setFeatures] = useState<Record<string, boolean>>({});
+  const [versionInfo, setVersionInfo] = useState<any>(null);
   const navigate = useNavigate();
   const location = useLocation();
   const user = getUser();
@@ -39,6 +40,7 @@ export default function MainLayout() {
     getBranding().then((res: any) => {
       setFeatures(res?.features || {});
     }).catch(() => {});
+    getVersion().then(setVersionInfo).catch(() => {});
   }, []);
 
   // Map feature flags to menu keys that should be hidden when the feature is disabled
@@ -172,6 +174,14 @@ export default function MainLayout() {
             }
           }}
         />
+        {!collapsed && versionInfo && (
+          <div style={{
+            padding: '8px 16px', fontSize: 11, color: 'rgba(255,255,255,0.3)',
+            borderTop: '1px solid rgba(255,255,255,0.06)', textAlign: 'center',
+          }}>
+            v{versionInfo.project_version}
+          </div>
+        )}
       </Sider>
       <Layout>
         <Header style={{