Merge upstream SagerNet/sing-box-for-android dev into dev (1.14.0-alpha.45)

Brings the app from 1.13.11 to 1.14.0-alpha.45, matching the sing-box core
now targeted by omv-dijiang. Fork customizations preserved: private
release.keystore and gradle heap limit (-Xmx4096m).

Dropped the 'temporary fix for building' neighbor-monitor stubs in
VPNService/ProxyService — upstream's new PlatformInterfaceWrapper now
provides the real startNeighborMonitor/closeNeighborMonitor implementations,
so the empty stubs would have overridden them.

gradle.properties

@@ -24,3 +24,9 @@ android.nonTransitiveRClass=true
 # Keep explicit Kotlin Gradle plugins enabled for current build scripts/plugins.
 android.newDsl=false
 android.builtInKotlin=false
+
+# Properties used by third_party/termux-app modules
+compileSdkVersion=36
+minSdkVersion=21
+targetSdkVersion=35
+ndkVersion=28.0.13004108