fix(reports): fix churn query crash and improve error reporting (#51)

The /api/reports/clients endpoint was crashing with a 500 on every request
because a raw JavaScript Date passed into a sql template literal in .having()
cannot be serialized by postgres-js. The fix serializes it as an ISO string
with an explicit ::timestamptz cast.

Also adds reportsRouter.onError() and improves the frontend error message
to surface which specific endpoint failed and why.

Fixes #49
Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/api/src/routes/reports.ts

@@ -16,6 +16,11 @@ import {
 
 export const reportsRouter = new Hono();
 
+reportsRouter.onError((err, c) => {
+  console.error("[reports] unhandled error:", err);
+  return c.json({ error: "Internal server error", message: err.message }, 500);
+});
+
 // ─── Helpers ──────────────────────────────────────────────────────────────────
 
 function parseDate(value: string | undefined, fallback: Date): Date {