FRE-622: Wire analytics services to tRPC API layer with comprehensive router

Create analytics-router.ts with ~30 tRPC endpoints for KPI management, alert
rules, scheduled reports, cohort analysis, and NPS survey integration.
Register router in index.ts under 'analytics' namespace. Fix pre-existing
bugs in service files: snake_case to camelCase conversion, missing non-null
assertions, and incorrect DB access patterns.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/lib/analytics/report-generator.ts

@@ -178,7 +178,7 @@ export async function createScheduledReport(
     lastRunAt: null,
     nextRunAt: computeNextRun(input.schedule),
   }).returning();
-  return result[0];
+  return result[0]!;
 }
 
 export async function getActiveScheduledReports(