fix(insight): count analytics totals independently

[NgoQuocViet2001]

Summary

• count analytics totals with dedicated aggregate queries instead of capped recent detail lists
• keep recent errors/prompts/tasks capped for dashboard detail sections
• add an Insight API regression test for capped detail lists vs uncapped totals

Problem

/api/analytics used the recent detail arrays to calculate totalErrors, totalPrompts, and totalTasks. Those arrays are intentionally capped at 20 rows for display, so dashboard KPI totals could be underreported when there were more matching records.

Validation

• pnpm exec vitest run tests/analytics/insight-cors.test.ts --reporter=dot
• pnpm exec vitest run tests/core/server.test.ts -t 'ctx_insight|insight-cache' --reporter=dot
• pnpm run build
• manual context-mode insight check: analytics error total matches category analytics error total