feat: add version API and solar KPI endpoint (v1.4.0)

New endpoints:
- GET /api/v1/version — returns VERSIONS.json (no auth required)
  For field engineers to check platform version from login page
- GET /api/v1/kpi/solar — returns PR, self-consumption rate,
  equivalent utilization hours, and daily revenue
  Handles station-level vs device-level data deduplication

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

VERSIONS.json

@@ -1,6 +1,6 @@
 {
   "project": "ems-core",
-  "project_version": "1.3.0",
+  "project_version": "1.4.0",
   "last_updated": "2026-04-06",
-  "notes": "Generic defaults, dashboard energy fallback, PV device type filter fix"
+  "notes": "Version API, solar KPI endpoint (PR, equiv hours, revenue, self-consumption)"
 }