crush33: back-to-scanner links + release v0.3.0 (versionCode 3)

Added "← Back to the scan app" on the crush33 unlock screen and a
"← Scanner" link in the admin hub top bar (both -> /).

v0.3.0 rolls up everything since v0.2.0: the /crush33 admin hub
(sidebar, admin-only donor lookup, wipe/switch danger zone with
confirm modals), removal of the /comp route, drawer no longer shows
crush33, the customer_name / voucher-count / ticketless-order webhook
fixes, ice bag fix, and the Adults/Youth/Kids gate panel.

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

app/app.json

@@ -2,7 +2,7 @@
   "expo": {
     "name": "Camp Scan",
     "slug": "camptickets",
-    "version": "0.2.0",
+    "version": "0.3.0",
     "orientation": "portrait",
     "scheme": "campscan",
     "userInterfaceStyle": "automatic",
@@ -10,7 +10,7 @@
     "icon": "./assets/icon.png",
     "android": {
       "package": "top.mowden.campscan",
-      "versionCode": 2,
+      "versionCode": 3,
       "adaptiveIcon": {
         "foregroundImage": "./assets/adaptive-icon.png",
         "backgroundColor": "#0f1a12"