feat(backend): init aris-backend with Hono

- Add apps/aris-backend package with Hono server
- Add /health endpoint
- Add backend-spec.md with design decisions

Co-authored-by: Ona <no-reply@ona.com>

apps/aris-backend/src/index.ts

@@ -0,0 +1,10 @@
+import { Hono } from "hono"
+
+const app = new Hono()
+
+app.get("/health", (c) => c.json({ status: "ok" }))
+
+export default {
+	port: 3000,
+	fetch: app.fetch,
+}