Surface self-updates through the regular updates list

Fold Aurora Store's self-update back into the existing update pipeline
instead of a dedicated sheet/viewmodel/helper. The feed entry is mapped
to a regular App and added to the update list, reusing the standard
download + install path; it is never auto-installed silently.

- Add a dedicated "Self-update" section in the Updates tab with the
  app-details navigation disabled (it's served from the Aurora OSS feed).
- Gate eligibility via PackageUtil.isSelfUpdateSupported(): vanilla/preload
  flavors, not debug, not F-Droid (huawei excluded by flavor).
- Add a build-aware Settings toggle as the opt-out, removing the row
  immediately when disabled.
- Exempt nightly self-updates from deleteInvalidUpdates (static version
  code) and drop any stale self-update row when none is offered, so a
  phantom update doesn't linger after a self-install.

app/src/main/java/com/aurora/Constants.kt

@@ -37,7 +37,8 @@ object Constants {
 
     const val SHARE_URL = "https://play.google.com/store/apps/details?id="
 
-    const val UPDATE_URL_STABLE = "https://gitlab.com/AuroraOSS/AuroraStore/raw/master/updates.json"
+    const val UPDATE_URL_VANILLA =
+        "https://auroraoss.com/downloads/AuroraStore/Feeds/release_feed.json"
     const val UPDATE_URL_NIGHTLY =
         "https://auroraoss.com/downloads/AuroraStore/Feeds/nightly_feed.json"