Federation, note modal, save-to-device, onboarding fixes + UI polish

- Configurable name authority (Settings → Identity → Name authority): bare
  names resolve there, own-domain names show bare, foreign verified names show
  'name · domain' with a check — no '@' anywhere. Lets bob@otherdomain pay
  alice@goblin.st. Home domain derived from the configured server.
- Note entry is now a modal that floats above the soft keyboard (dimmed
  backdrop) instead of an inline editor the keyboard covered.
- Backup export SAVES to a chosen location (Android CREATE_DOCUMENT / desktop
  save dialog) instead of opening the share sheet.
- Onboarding status-bar icons are legible again (white on the dark surface,
  not black); identity step is less wordy and drops the '@' prefix; claiming a
  name during onboarding now republishes kind 0 so it's visible immediately.
- App-open name re-verify sweep (persisted, runs if >78s since last).
- Advanced 'Manage node connection' opens GRIM's native Connections UI.
- Manual slatepack paste: removed the QR icon. Pay screen: bolder, bigger ツ.
- Localized new strings across 6 locales.

android/app/src/main/java/mw/gri/android/MainActivity.java

@@ -69,6 +69,9 @@ public class MainActivity extends GameActivity {
 
     private ActivityResultLauncher<Intent> mFilePickResult = null;
     private ActivityResultLauncher<Intent> mOpenFilePermissionsResult = null;
+    private ActivityResultLauncher<Intent> mFileSaveResult = null;
+    // Source path (in the share cache) staged by Rust for the next saveFile().
+    private String mPendingSavePath = null;
 
     @SuppressLint("UnspecifiedRegisterReceiverFlag")
     @Override
@@ -145,6 +148,32 @@ public class MainActivity extends GameActivity {
                     }
                 });
 
+        // Register file SAVE result (Storage Access Framework CREATE_DOCUMENT):
+        // copy the staged source file into the user-chosen document.
+        mFileSaveResult = registerForActivityResult(
+                new ActivityResultContracts.StartActivityForResult(),
+                result -> {
+                    String src = mPendingSavePath;
+                    mPendingSavePath = null;
+                    if (result.getResultCode() == Activity.RESULT_OK && src != null) {
+                        Intent data = result.getData();
+                        if (data != null && data.getData() != null) {
+                            Uri uri = data.getData();
+                            try (InputStream is = new FileInputStream(new File(src));
+                                 OutputStream os = getContentResolver().openOutputStream(uri)) {
+                                byte[] buffer = new byte[4096];
+                                int length;
+                                while (is != null && (length = is.read(buffer)) > 0) {
+                                    os.write(buffer, 0, length);
+                                }
+                                if (os != null) os.flush();
+                            } catch (Exception e) {
+                                Log.e("grim", e.toString());
+                            }
+                        }
+                    }
+                });
+
         // Listener for display insets (cutouts) to pass values into native code.
         View content = getWindow().getDecorView().findViewById(android.R.id.content);
         ViewCompat.setOnApplyWindowInsetsListener(content, (v, insets) -> {
@@ -510,6 +539,23 @@ public class MainActivity extends GameActivity {
         startActivity(Intent.createChooser(intent, "Share data"));
     }
 
+    // Called from native code to SAVE a staged file to a user-chosen location.
+    // Launches the Storage Access Framework create-document picker; the result
+    // handler copies the staged source file into the chosen document.
+    public void saveFile(String path, String name) {
+        mPendingSavePath = path;
+        Intent intent = new Intent(Intent.ACTION_CREATE_DOCUMENT);
+        intent.addCategory(Intent.CATEGORY_OPENABLE);
+        intent.setType("application/octet-stream");
+        intent.putExtra(Intent.EXTRA_TITLE, name);
+        try {
+            mFileSaveResult.launch(intent);
+        } catch (android.content.ActivityNotFoundException ex) {
+            Log.e("grim", ex.toString());
+            mPendingSavePath = null;
+        }
+    }
+
     // Called from native code to share plain text (e.g. a payment link) via the
     // system share sheet.
     public void shareText(String text) {