fix(android): unblock build + JNI bridge for the default Android target

[proggeramlug]

Summary

Bringing up a Perry-targeted app on the Android emulator from current
main surfaced a chain of breakages — the Android target wasn't
compilable, dlopenable, or runnable end-to-end. None of these changes
are Android-specific behavior tweaks; each one repairs a contract that
other platforms already honor.

Verified on a Pixel_8 emulator (API 35, arm64-v8a, NDK 30): app now
compiles cleanly, links cleanly, passes dlopen, runs Java_…_nativeMain
through to App.run()/setContentView, and starts the 8 ms timer pump.

Compile / link fixes

File	Fix
crates/perry-ui-android/src/lib.rs (perry_system_take_screenshot)	Function referenced crate::screenshot::… unconditionally but pub mod screenshot; is #[cfg(feature = \"geisterhand\")]. Default builds failed with E0433. Cfg-gate the function; non-geisterhand returns an empty base64 string, matching the documented contract.
crates/perry-ui-android/src/lib.rs	Added no-op perry_ui_lazyvstack_set_row_height (matches the iOS stub). Without it, every app that calls lazyvstackSetRowHeight(list, …) failed dlopen(libperry_app.so) with cannot locate symbol.
crates/perry-runtime/src/gc.rs	Added no-op js_gc_note_slot_layout / js_gc_write_barriers_emitted. The codegen emits unconditional refs; no crate provided them, so dlopen died on the first. No-op honors the contract (the GC functions fine without per-slot layout notes).
android-build/.../PerryBridge.kt (granted expression)	Kotlin syntax error: == / || at line start. Moved operators to line ends.
android-build/.../PerryBridge.kt (richTextToggleSpan)	Kotlin 2.0.21 rejects inline fun lambdas called from inside uiHandler.post { … } without crossinline. Added on factory and matches.
android-build/.../PerryBridge.kt (nativeNotification{Tap,Token,Receive,BackgroundReceive})	Added the four @JvmStatic external fun declarations. PerryFirebaseMessagingService / PerryNotificationReceiver referenced them; the Rust side already exports the matching JNI symbols in perry-ui-android/src/system.rs.

JNI-bridge fixes

Area	Fix
crates/perry-ui-android/src/widgets/securefield.rs	Called PerryBridge.setTextWatcher but the actual entrypoint is setTextChangedCallback (textfield.rs / textarea.rs use it). Mismatch aborted with JNI DETECTED ERROR … NoSuchMethodError the moment a SecureField was constructed. Renamed the JNI call to match.
android-build/.../PerryBridge.kt (deep links)	The Kotlin side had no deep-link implementation. perry-ui-android/src/deeplinks.rs documents the contract: register a handler key via PerryBridge.appOnOpenUrl(J)V, read the cold-start URL via appGetLaunchUrl()Ljava/lang/String;, dispatch URLs back into JS through nativeInvokeDeepLinkCallback(key, url, source). None existed. set_handler() discards the JNI result, so the NoSuchMethodError exception stayed pending and the next JNI op (NewLocalRef from NavStack get_activity) tripped CheckJNI → app abort. Added: appOnOpenUrl / appGetLaunchUrl / deliverDeepLinkUrl @JvmStatic methods + the external fun nativeInvokeDeepLinkCallback declaration on PerryBridge.
android-build/.../PerryActivity.kt	Captures intent?.data in onCreate (cold start) and overrides onNewIntent (warm), routing both through PerryBridge.deliverDeepLinkUrl(url, source).

Known follow-up — not in this PR

After all of the above the app passes dlopen, nativeMain runs to
completion, the NavStack tree is built, root view is attached, and the
8 ms timer pump starts. ~140 ms later the first JS-side callback fires
and the HWUI worker aborts with:

F libc    : FORTIFY: pthread_mutex_lock called on a destroyed mutex (0x...)
F libc    : Fatal signal 6 (SIGABRT), code -1 (SI_QUEUE) in tid N (hwuiTask1)

No tombstone is produced (FORTIFY aborts skip the standard debuggerd
dump path), no Java exception, no JNI message. Likely a render-side
use-after-free of a sync primitive — needs lldb / ASAN to localize.
Filing as a separate issue.

Test plan

• cargo build --release -p perry-ui-android -p perry-runtime --target aarch64-linux-android (NDK 30, with the cc-rs unversioned-clang shim documented in the issue tracker) — clean build
• perry compile src/main.ts --target android -o libperry_app.so — links, no missing symbols
• cd android-build && ./gradlew assembleDebug — BUILD SUCCESSFUL, APK produced
• adb install + am start — no UnsatisfiedLinkError, no JNI NoSuchMethodError, no perry-native-thread tombstone; reaches attach_root_to_activity: setContentView called + start_timer_pump
• Visual audit on emulator — blocked by the HWUI mutex abort (separate issue)