Add shared PasswordVisibilityToggle design-system component

Extract the show/hide password trailing-icon into a reusable
PasswordVisibilityToggle so every password field reveals plaintext the
same way and announces the same a11y labels. Reuse it from the login and
reset-identity password fields. Pure refactor, no behaviour change.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

libraries/designsystem/src/main/kotlin/io/element/android/libraries/designsystem/theme/components/PasswordVisibilityToggle.kt

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2026 Element Creations Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+package io.element.android.libraries.designsystem.theme.components
+
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.layout.Box
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.res.stringResource
+import io.element.android.compound.tokens.generated.CompoundIcons
+import io.element.android.libraries.ui.strings.CommonStrings
+
+/**
+ * Show/hide toggle for a password [TextField], intended for its `trailingIcon` slot.
+ * Shared so every password field reveals plaintext the same way and announces the
+ * same accessibility labels.
+ */
+@Composable
+fun PasswordVisibilityToggle(
+    visible: Boolean,
+    onToggle: () -> Unit,
+    modifier: Modifier = Modifier,
+) {
+    Box(modifier.clickable(onClick = onToggle)) {
+        Icon(
+            imageVector = if (visible) CompoundIcons.VisibilityOn() else CompoundIcons.VisibilityOff(),
+            contentDescription = stringResource(
+                if (visible) CommonStrings.a11y_hide_password else CommonStrings.a11y_show_password
+            ),
+        )
+    }
+}