feat: add high-contrast theme with accessible message bubbles (#5135)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

core/domain/src/commonMain/kotlin/org/meshtastic/core/domain/usecase/settings/SetContrastLevelUseCase.kt

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2025-2026 Meshtastic LLC
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package org.meshtastic.core.domain.usecase.settings
+
+import org.koin.core.annotation.Single
+import org.meshtastic.core.repository.UiPrefs
+
+@Single
+open class SetContrastLevelUseCase constructor(private val uiPrefs: UiPrefs) {
+    operator fun invoke(value: Int) {
+        uiPrefs.setContrastLevel(value)
+    }
+}