fix(android): keep the toolbar out of the status and navigation bars (Issue #50)

NativeActivity draws the whole window, also below the system bars, so the
top toolbar button lay under the status bar and taps there went to
Android (no other notebook could be opened). InkActivity now reports the
system bar and cutout insets; the app shrinks egui's screen rect to the
free area and adds the side insets to the page centering. The page itself
still scrolls below the bars.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/android_bridge.rs

@@ -6,6 +6,7 @@
 //! below, possibly on another thread, so they only queue messages and wake the event loop.
 
 use std::path::PathBuf;
+use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::Mutex;
 
 use jni::objects::{JObject, JString, JValue};
@@ -24,15 +25,23 @@ enum Message {
 static MESSAGES: Mutex<Vec<Message>> = Mutex::new(Vec::new());
 /// What the open file dialog is for
 static PICKING: Mutex<Option<PickerKind>> = Mutex::new(None);
+/// Window edges covered by system bars or cutouts (left, top, right, bottom; pixels)
+static INSETS: Mutex<[f32; 4]> = Mutex::new([0.0; 4]);
+/// The insets changed since the last frame
+static INSETS_CHANGED: AtomicBool = AtomicBool::new(false);
+
+fn wake() {
+    if let Some(app) = crate::platform::android_app() {
+        app.create_waker().wake();
+    }
+}
 
 fn push(message: Message) {
     MESSAGES
         .lock()
         .unwrap_or_else(|e| e.into_inner())
         .push(message);
-    if let Some(app) = crate::platform::android_app() {
-        app.create_waker().wake();
-    }
+    wake();
 }
 
 #[no_mangle]
@@ -75,16 +84,39 @@ pub extern "system" fn Java_eu_pansi_inknotes_InkActivity_nativeFilePicked(
     push(Message::Picked(path));
 }
 
-/// Is a message waiting (then the app draws a new frame to take it)?
+#[no_mangle]
+pub extern "system" fn Java_eu_pansi_inknotes_InkActivity_nativeSetInsets(
+    _env: JNIEnv,
+    _class: JObject,
+    left: jint,
+    top: jint,
+    right: jint,
+    bottom: jint,
+) {
+    let insets = [left, top, right, bottom].map(|v| v.max(0) as f32);
+    *INSETS.lock().unwrap_or_else(|e| e.into_inner()) = insets;
+    INSETS_CHANGED.store(true, Ordering::Relaxed);
+    wake();
+}
+
+/// Window edges covered by the status bar, the navigation bar or display cutouts (left, top,
+/// right, bottom; physical pixels)
+pub fn insets() -> [f32; 4] {
+    *INSETS.lock().unwrap_or_else(|e| e.into_inner())
+}
+
+/// Is a message waiting or did the insets change (then the app draws a new frame)?
 pub fn has_messages() -> bool {
-    !MESSAGES
-        .lock()
-        .unwrap_or_else(|e| e.into_inner())
-        .is_empty()
+    INSETS_CHANGED.load(Ordering::Relaxed)
+        || !MESSAGES
+            .lock()
+            .unwrap_or_else(|e| e.into_inner())
+            .is_empty()
 }
 
 /// Typed text and deletions as egui input, and the action for a picked file.
 pub fn take_messages() -> (Vec<egui::Event>, Vec<UiAction>) {
+    INSETS_CHANGED.store(false, Ordering::Relaxed);
     let messages = std::mem::take(&mut *MESSAGES.lock().unwrap_or_else(|e| e.into_inner()));
     let mut events = Vec::new();
     let mut actions = Vec::new();