Support deferred deep links for survey QR codes

[rfontanarosa]

Web now routes survey QR codes through /android/survey/. The Android app needs to handle both cases:

1. App installed — register an intent filter (verified App Link) for https:///android/survey/ and open that survey.
2. App not installed — after install from Play Store, read the install referrer (survey_id=) via the Install Referrer API (https://developer.android.com/google/play/installreferrer), parse it, and open the survey on first launch (run once, degrade gracefully if absent).

Play Store URL web produces: …/details?id=&referrer=survey_id%3D (decode before parsing).