Fix Android 11 Keystore execution: Init framework and spoof UID 1000 (#85)

This commit resolves `KeyStore` API failures on Android 11 when running as a standalone CLI executable (UID 0), addressing both environment initialization and permission denial issues.

1. Initialize Android Framework Environment:
   Android 11 Keystore APIs expect a fully initialized application context and a Main Looper, which are missing in a raw root process. This patch:
   - Manually bootstraps `ActivityThread` via `systemMain()`.
   - Initializes `Looper.prepareMainLooper()`.
   - Injects a dummy `Application` object attached to the system context to satisfy `KeyStore.getApplicationContext()` checks.
   - Updates framework stubs to allow compilation of these hidden APIs.

2. Bypass Keystore Permission Checks via UID Spoofing:
   `KeyStoreService::generateKey` enforces the `P_INSERT` permission. Analysis of `permissions.cpp` reveals that UID 0 (Root) is explicitly denied this permission (granted only `P_GET`), whereas UID 1000 (System) holds all permissions (`~0`).
   
   To bypass this restriction, the binder interceptor now detects transactions originating from UID 0 and rewrites the `sender_euid` to 1000. This fools `KeyStoreService` into granting the request.
 
3. Refactor Execution Loop:
   Replaces the previous `Thread.sleep()` maintenance loop with `Looper.loop()`.

stub/src/main/java/android/app/ActivityThread.java

@@ -4,4 +4,12 @@ public class ActivityThread {
     public static void initializeMainlineModules() {
         throw new UnsupportedOperationException("STUB!");
     }
+
+    public static ActivityThread systemMain() {
+        throw new UnsupportedOperationException("STUB!");
+    }
+
+    public ContextImpl getSystemContext() {
+        throw new UnsupportedOperationException("STUB!");
+    }
 }

stub/src/main/java/android/app/ContextImpl.java

@@ -0,0 +1,4 @@
+package android.app;
+
+public class ContextImpl {
+}