chore: add BUYOFF.md template, remove stale backend/ directory

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

BUYOFF.md

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+# Deployment Buyoff Checklist
+
+**Customer:** 天普大兴园区 (Tianpu Daxing Zero-Carbon Park)
+**Project:** tp-ems
+**Date:** _______________
+**Performed by:** _______________
+**Environment:** [ ] Staging  [ ] Production
+
+---
+
+## Phase 1: Infrastructure
+
+- [ ] PostgreSQL running and accessible
+- [ ] Redis running and accessible
+- [ ] All database migrations applied successfully
+- [ ] Seed data loaded (device types, default config)
+- [ ] Admin user created and can log in
+- [ ] `.env` file configured with correct values
+- [ ] All required ports open and not conflicting
+
+## Phase 2: Backend API
+
+- [ ] `GET /health` returns OK
+- [ ] Auth endpoints working (login, token refresh, logout)
+- [ ] Device stats endpoints return data
+- [ ] Dashboard summary endpoint returns data
+- [ ] Collectors are registered and configured
+- [ ] Branding endpoint returns Tianpu config
+- [ ] Swagger docs accessible at `/docs`
+- [ ] Version endpoint returns correct version
+- [ ] Solar KPI endpoints return data (PR, equivalent hours, revenue)
+
+## Phase 3: Data Collection
+
+- [ ] Collectors connected to data source (iSolarCloud API)
+- [ ] Data being collected on schedule
+- [ ] All expected devices showing online
+- [ ] Energy data (kWh) being recorded
+- [ ] No collector errors in logs
+- [ ] Rate limits respected (no 429 errors)
+
+## Phase 3.5: Data Pipeline & Accuracy
+
+- [ ] PV power values match iSolarCloud source within 5%
+- [ ] PV energy values match iSolarCloud source within 5%
+- [ ] Heat pump power/energy values match source within 5%
+- [ ] No double-counting between station-level and device-level data
+- [ ] Daily summary aggregation correct
+- [ ] Unit conversions correct (W/kW/MW, Wh/kWh/MWh)
+- [ ] `scripts/validate_data.py` passes with no errors
+
+### Data Accuracy Cross-Reference Table
+
+| Metric | Source Value | EMS Value | Difference | Within 5%? |
+|--------|-------------|-----------|------------|------------|
+| PV Daily Energy (kWh) | | | | [ ] |
+| PV Current Power (kW) | | | | [ ] |
+| Heat Pump Daily Energy (kWh) | | | | [ ] |
+| Heat Pump Current Power (kW) | | | | [ ] |
+| Total Grid Import (kWh) | | | | [ ] |
+| Total Grid Export (kWh) | | | | [ ] |
+| Self-Consumption Rate (%) | | | | [ ] |
+| PV Performance Ratio (%) | | | | [ ] |
+
+**Source API checked:** _______________
+**Timestamp of comparison:** _______________
+
+## Phase 4: Frontend Pages
+
+- [ ] Login page loads and authentication works
+- [ ] Dashboard / Overview page
+- [ ] Monitoring page (real-time)
+- [ ] Device list page
+- [ ] Analysis page
+- [ ] Alarm management page
+- [ ] Carbon tracking page
+- [ ] Reports page
+- [ ] Quota management page
+- [ ] Maintenance / work orders page
+- [ ] Data query page
+- [ ] Prediction page
+- [ ] System management page (users, roles)
+- [ ] Energy strategy page
+- [ ] AI operations page
+- [ ] Big screen display page
+
+## Phase 5: Feature Flags
+
+- [ ] Disabled features are hidden from navigation
+- [ ] Disabled feature routes return 404 or redirect
+- [ ] All enabled features are functional
+- [ ] Feature flag config matches customer requirements
+
+## Phase 6: Dashboard Charts & Widgets
+
+- [ ] PV power curve (real-time)
+- [ ] Heat pump power/status
+- [ ] Carbon reduction metrics
+- [ ] Active alarms count
+- [ ] Load curve chart
+- [ ] Device status pie chart (online/offline/alarm)
+- [ ] Energy flow diagram (Sankey or animated)
+- [ ] Energy overview bar chart
+- [ ] PV generation trend
+- [ ] Installed capacity display
+- [ ] Recent alarms list
+- [ ] Performance Ratio (PR) gauge
+- [ ] Equivalent full-load hours
+- [ ] Estimated revenue
+- [ ] Self-consumption ratio
+
+**All charts showing real data (not zeros or placeholders):** [ ] Yes  [ ] No
+
+## Phase 7: UI Interactions
+
+- [ ] Dark mode toggle works
+- [ ] Language switch (zh-CN / en-US) works
+- [ ] Sidebar navigation collapses/expands
+- [ ] Alarm bell shows notification count
+- [ ] User dropdown menu works
+- [ ] Logout clears session
+- [ ] Pagination works on list pages
+- [ ] CRUD operations work (create, read, update, delete)
+
+## Phase 8: Performance & Errors
+
+- [ ] No JavaScript errors in browser console
+- [ ] No failed API requests (check Network tab)
+- [ ] No unhandled backend exceptions in logs
+- [ ] Page load time < 3 seconds
+- [ ] WebSocket connections stable (if applicable)
+
+## Phase 9: Customer-Specific (Tianpu)
+
+- [ ] Customer name displays as "天普大兴园区"
+- [ ] Theme/branding matches Tianpu requirements
+- [ ] All Tianpu devices present in device list
+- [ ] Device models match physical installation
+- [ ] Electricity pricing config correct
+- [ ] Alarm rules configured for Tianpu thresholds
+- [ ] Carbon emission factor set correctly
+- [ ] Data source: iSolarCloud API configured with correct `ps_id`
+- [ ] Version displayed in UI matches deployed version
+- [ ] Feature flags match Tianpu scope
+- [ ] `ps_id` values correct for all Tianpu stations
+- [ ] Customer config volume/mount verified
+
+---
+
+## Sign-Off
+
+| Role | Name | Signature | Date |
+|------|------|-----------|------|
+| Developer | | | |
+| QA / Tester | | | |
+| Project Lead | | | |
+| Customer Rep | | | |
+
+### Notes
+
+_Use this space for any observations, deviations, or follow-up items:_
+
+1.
+2.
+3.
+
+---
+
+*Generated from EMS Deployment Buyoff Checklist template. All items must be checked before deployment is considered complete.*