feat: implement error handling and validation middleware, enhance result handling

Co-authored-by: Copilot <copilot@github.com>

apps/backend/src/lib/http/problem-details.ts

@@ -0,0 +1,10 @@
+import type { ContentfulStatusCode } from 'hono/utils/http-status'
+
+export type ProblemDetails = {
+  type: string
+  title: string
+  status: ContentfulStatusCode
+  detail?: string
+  instance?: string
+  errors?: Record<string, string[]>
+}