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/package.json

@@ -12,12 +12,22 @@
       "import": "./dist/index.js"
     }
   },
-  "files": ["dist", "src", "README.md"],
+  "files": [
+    "dist",
+    "src",
+    "README.md"
+  ],
   "scripts": {
     "build": "tsc -p tsconfig.json",
-    "typecheck": "tsc -p tsconfig.json --noEmit"
+    "typecheck": "tsc -p tsconfig.json --noEmit",
+    "test": "node --test test/*.test.mjs"
   },
-  "keywords": ["parksmarter", "parking", "ips", "api-client"],
+  "keywords": [
+    "parksmarter",
+    "parking",
+    "ips",
+    "api-client"
+  ],
   "license": "MIT",
   "devDependencies": {
     "typescript": "^5.4.0"