feat(tracking): add sf_tracking package and instrument legacy module

Introduces packages/sf_tracking — a multi-client, GDPR-first analytics layer with feature mixins, a GoRouter listener for automatic screen views, and a user properties helper that runs on login.
Wires the package into the legacy module 61 events

apps/mobile_app/android/app/build.gradle.kts

@@ -27,6 +27,9 @@ android {
     compileOptions {
         sourceCompatibility = JavaVersion.VERSION_11
         targetCompatibility = JavaVersion.VERSION_11
+        // Required by flutter_local_notifications (and any future libs that
+        // need Java 8+ APIs on older Android API levels).
+        isCoreLibraryDesugaringEnabled = true
     }
 
     kotlinOptions {
@@ -95,3 +98,7 @@ android {
 flutter {
     source = "../.."
 }
+
+dependencies {
+    coreLibraryDesugaring("com.android.tools:desugar_jdk_libs:2.1.4")
+}