feat(android): wire Android Keystore JNI via OnceLock

Remove the dependency on bevy::android::ANDROID_APP inside
android_keystore.rs. Instead, solitaire_data owns a process-wide
OnceLock<JavaVM> initialised by a new pub fn init_android_jvm().
solitaire_app calls it from android_main before run() so JNI is
ready before any auth-token operation can execute.

- android_keystore: drop ANDROID_APP import; add ANDROID_JVM OnceLock
  and init_android_jvm(vm_ptr: *mut c_void)
- solitaire_data/lib.rs: re-export init_android_jvm for android target
- auth_tokens.rs: update doc comment (Android backend is now complete)
- solitaire_app/lib.rs: call init_android_jvm from android_main

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

solitaire_app/src/lib.rs

@@ -65,10 +65,9 @@ pub fn run() {
     // operations will fail gracefully with TokenError::KeychainUnavailable.
     //
     // Android: `keyring` isn't compiled in (its `rpassword` transitive
-    // pulls a libc symbol Android's bionic doesn't expose). `auth_tokens`
-    // ships an Android stub that returns KeychainUnavailable for every
-    // call — the runtime behaviour is "session login required each launch"
-    // until we wire Android Keystore via JNI in the Phase-Android round.
+    // pulls a libc symbol Android's bionic doesn't expose). The Android
+    // auth-token path uses Android Keystore via JNI; `android_main` passes
+    // the process JavaVM pointer into `solitaire_data` before `run()`.
     #[cfg(not(target_os = "android"))]
     if let Err(e) = keyring::use_native_store(true) {
         eprintln!(
@@ -366,6 +365,10 @@ fn set_window_icon(
 #[cfg(target_os = "android")]
 #[unsafe(no_mangle)]
 fn android_main(android_app: bevy::android::android_activity::AndroidApp) {
+    let vm_ptr = android_app.vm_as_ptr().cast();
+    if let Err(e) = solitaire_data::init_android_jvm(vm_ptr) {
+        eprintln!("warn: could not initialise Android Keystore JNI ({e})");
+    }
     let _ = bevy::android::ANDROID_APP.set(android_app);
     run();
 }