Add GET /analytics/trends endpoint returning per-company analysis
counts by month and analysis type distribution over time. Render
these as a line chart (analyses per company) and stacked bar chart
(analysis types) on the Analytics page using recharts.
Closesleeworks-agents/SPARC#24
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>