v0.2.6: fix kiosk-code scan resolution + add zone QR asset

ScanScreen.lookupCode tried getMetersByScannerCode first and let its thrown
error-envelope abort the whole lookup, so the getMetersByZoneName fallback never
ran; it also sent ZoneName in the scanned case (the API is case-sensitive — the
official app lowercases). Confirmed via live mitmproxy capture of the official
app: a scanned code resolves through ScannerCode, and ZoneName=dl (lowercase)
returns the zone.

Now tries ScannerCode -> ZoneName -> zonename(lowercased) -> TerminalSerNo, each
independent and non-fatal; only reports "Lookup failed" if every attempt errored.

Adds docs/zone-qr/ with the DL-Sandpoint QR (encodes ScannerCode "DL", works in
both BigBrainParking and the official app) and a how-to.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/app.json

@@ -3,14 +3,14 @@
     "name": "BigBrainParking",
     "slug": "bigbrainparking",
     "scheme": "bigbrainparking",
-    "version": "0.2.5",
+    "version": "0.2.6",
     "orientation": "portrait",
     "userInterfaceStyle": "automatic",
     "newArchEnabled": true,
     "icon": "./assets/icon.png",
     "android": {
       "package": "top.mowden.bigbrainparking",
-      "versionCode": 15,
+      "versionCode": 16,
       "edgeToEdgeEnabled": true,
       "adaptiveIcon": {
         "foregroundImage": "./assets/adaptive-icon.png",