feat: string monitoring, ROI simulator, knowledge base, stubs (v1.6.0)

New functional pages:
- String-Level Monitoring — simulated string data with heatmap,
  comparison chart, status table (Under Construction banner)
- ROI Simulator — 25-year investment return calculator with
  IRR, NPV, payback period, cash flow chart
- Knowledge Base — O&M wiki with 5 articles, search, categories
- Mobile responsive — sidebar auto-collapse on small screens

Under Construction stubs:
- I-V Curve Diagnosis — demo chart, 4 feature preview cards
- Remote Device Configuration — parameter preview, disabled
  actions, v2.0+ roadmap timeline

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

VERSIONS.json

@@ -1,9 +1,9 @@
 {
   "project": "zpark-ems",
-  "project_version": "1.5.0",
+  "project_version": "1.6.0",
   "customer": "Z-Park 中关村医疗器械园",
   "core_version": "1.4.0",
   "frontend_template_version": "1.4.0",
   "last_updated": "2026-04-06",
-  "notes": "Energy flow diagram, weather widget, curve templates, device comparison, dispersion analysis, PWA, alarm subscriptions"
+  "notes": "String monitoring, I-V diagnosis stub, ROI simulator, knowledge base, remote config stub, mobile responsive"
 }