feat: build analytics dashboard for energy generation statistics (#350)

[Julianemeka]

Built a comprehensive energy analytics dashboard for cooperatives and users.

Changes:

• Database: Added get_cooperative_trends and get_cooperative_meter_stats RPC functions for efficient time-series aggregation.
• API: Enhanced /api/cooperative/stats to support date range filtering, custom granularity (day/month/year), and per-meter performance metrics.
• Frontend:
  • Implemented Generation Trend chart (Area chart for kWh).
  • Implemented Certificates Activity chart (Line chart for Issued vs. Retired).
  • Added Range Presets (30d, 90d, YTD, All Time).
  • Added Per-Meter Performance table with generation share and certificate counts.
  • Implemented CSV Export for trend data and meter performance.
  • Revamped dashboard layout for better information density and responsiveness.

Closes #350

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