feat: add shadcn calendar primitives

frontend/tests/birth-date-picker-contract.test.ts

@@ -0,0 +1,11 @@
+import assert from "node:assert/strict"
+import { existsSync, readFileSync } from "node:fs"
+import test from "node:test"
+
+const packageJson = readFileSync(new URL("../package.json", import.meta.url), "utf8")
+
+test("provides the shadcn calendar and popover primitives", () => {
+  assert.equal(existsSync(new URL("../src/components/ui/calendar.tsx", import.meta.url)), true)
+  assert.equal(existsSync(new URL("../src/components/ui/popover.tsx", import.meta.url)), true)
+  assert.match(packageJson, /"react-day-picker"/)
+})