v0.1.5: detect free windows in the estimate fallback + add API tests

App:
- When the single-estimate fallback sees MaxTime 0 (or an all-$0.00 ladder),
  show "Parking is currently free" instead of a bogus $0.00 purchase ladder.
  Free-detection extracted to tested client helpers (isFreeEstimate/ladderAllFree).

Client + tests (node:test, zero deps):
- src/estimates.ts: pure isFreeEstimate/ladderAllFree helpers (exported).
- test/estimates + test/http (mocked fetch): headers, query serialization,
  error->ParkSmarterApiError, rolling Auth_Token refresh, 401 clears token.
- test/integration: live checks against the Sandpoint (DSB) zones; targets the
  `test` instance by default and SKIPS when it's unreachable (non-prod is
  IP-restricted -> 403). Verified 3/3 green against prodv2 read-only.
- CI runs `npm test` as a build gate.

Note: dev/stage/test instances return 403 "Web App - Unavailable" from the
public internet (IP-restricted). API schema is otherwise unchanged vs Jul 6.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

parksmarter-client/test/estimates.test.mjs

@@ -0,0 +1,32 @@
+// Pure unit tests for the estimate-classification helpers (no network).
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { isFreeEstimate, ladderAllFree } from '../dist/index.js';
+
+test('isFreeEstimate: MaxTime 0 is a free window', () => {
+  assert.equal(isFreeEstimate({ MaxTime: 0 }), true);
+  assert.equal(isFreeEstimate({ MaxTime: '0' }), true); // API sends numbers as strings
+});
+
+test('isFreeEstimate: positive MaxTime is a paid zone', () => {
+  assert.equal(isFreeEstimate({ MaxTime: 33 }), false);
+  assert.equal(isFreeEstimate({ MaxTime: '33' }), false);
+});
+
+test('isFreeEstimate: missing/null MaxTime => no paid time => free', () => {
+  assert.equal(isFreeEstimate({}), true);
+  assert.equal(isFreeEstimate(null), true);
+  assert.equal(isFreeEstimate(undefined), true);
+});
+
+test('ladderAllFree: every rung $0.00 => true', () => {
+  assert.equal(ladderAllFree([{ ParkingCost: '0.00' }, { ParkingCost: 0 }]), true);
+});
+
+test('ladderAllFree: any priced rung => false', () => {
+  assert.equal(ladderAllFree([{ ParkingCost: '0.00' }, { ParkingCost: '0.10' }]), false);
+});
+
+test('ladderAllFree: empty ladder => false (nothing to conclude)', () => {
+  assert.equal(ladderAllFree([]), false);
+});