Add Android Steam library artwork and supervised Lepton sessions

Generate five artwork slots, refresh VR shortcuts and managed collections, and retain a signal-aware launcher around setsid so stopping the wrapper cleans its container. Cover installation, artwork and launch cleanup offline; record the Steam client startup blocker for device verification.

Co-Authored-By: GPT-6 Astra <noreply@openai.com>

tests/fixtures/library/steam-responses.json

@@ -0,0 +1,12 @@
+{
+  "home": "/home/steamos",
+  "shortcuts": [
+    {
+      "appid": 3346865537,
+      "name": "Open Saber Plus"
+    }
+  ],
+  "configure": {
+    "warnings": []
+  }
+}