v0.2.4: fix countdown notification not appearing + wrong time-remaining

Countdown notification "nothing appears" on session start:
- The small icon was the adaptive launcher mipmap (applicationInfo.icon),
  which Android 13+/GrapheneOS rejects as an invalid notification small icon
  and drops the post silently. Ship a proper white-on-transparent vector
  small icon (bbp_stat_parking) inside the module and use it.
- showCountdown now returns a diagnostic string (posted / notifications
  disabled / exception) instead of swallowing failures; JS logs the branch,
  permission result, and native outcome to the in-app diagnostics log.
- Log the raw active-session payload in refreshSessionStatus (element shape
  was previously unconfirmed).

Time remaining showed "7694 min":
- API's TimeRemaining is SECONDS, not minutes. Format it as hours+minutes
  in SessionDetail; annotate the type.

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": "0.2.3",
+    "version": "0.2.4",
     "orientation": "portrait",
     "userInterfaceStyle": "automatic",
     "newArchEnabled": true,
     "icon": "./assets/icon.png",
     "android": {
       "package": "top.mowden.bigbrainparking",
-      "versionCode": 13,
+      "versionCode": 14,
       "edgeToEdgeEnabled": true,
       "adaptiveIcon": {
         "foregroundImage": "./assets/adaptive-icon.png",