fix(folio): add parseTypedAmount helper matching app's parseCents

Raw user input like "50" must become 5000 cents, not 50. The existing
parseDollarCents helper strips non-digits and so reads "50" as 50 cents,
which is correct for formatted balance text but off by 100x for raw
input from the amount field.

pkg/spec/test/folio-typed-amount.test.ts

@@ -0,0 +1,56 @@
+import assert from "node:assert/strict";
+import { test } from "node:test";
+
+import { parseTypedAmount } from "../../../examples/folio/sanderling/predicates.ts";
+
+test("empty string returns 0", () => {
+  assert.equal(parseTypedAmount(""), 0);
+});
+
+test("undefined returns 0", () => {
+  assert.equal(parseTypedAmount(undefined), 0);
+});
+
+test("null returns 0", () => {
+  assert.equal(parseTypedAmount(null), 0);
+});
+
+test("whole number 50 parses as 5000 cents", () => {
+  assert.equal(parseTypedAmount("50"), 5000);
+});
+
+test("decimal 5.50 parses as 550 cents", () => {
+  assert.equal(parseTypedAmount("5.50"), 550);
+});
+
+test("decimal 5.05 parses as 505 cents", () => {
+  assert.equal(parseTypedAmount("5.05"), 505);
+});
+
+test("one-decimal 0.5 parses as 50 cents", () => {
+  assert.equal(parseTypedAmount("0.5"), 50);
+});
+
+test("non-numeric returns 0", () => {
+  assert.equal(parseTypedAmount("abc"), 0);
+});
+
+test("too many decimals returns 0", () => {
+  assert.equal(parseTypedAmount("5.123"), 0);
+});
+
+test("zero returns 0", () => {
+  assert.equal(parseTypedAmount("0"), 0);
+});
+
+test("leading plus sign tolerated as positive", () => {
+  assert.equal(parseTypedAmount("+50"), 5000);
+});
+
+test("leading minus sign tolerated as positive", () => {
+  assert.equal(parseTypedAmount("-50"), 5000);
+});
+
+test("comma-separated thousands accepted", () => {
+  assert.equal(parseTypedAmount("1,234.56"), 123456);
+});