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>

VERSION

@@ -1 +1 @@
-1.3.0
+1.4.0