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

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

core/ui/src/commonMain/kotlin/org/meshtastic/core/ui/theme/ContrastLevel.kt

@@ -0,0 +1,44 @@
+/*
+ * 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.ui.theme
+
+import androidx.compose.runtime.staticCompositionLocalOf
+
+/**
+ * Application-wide contrast level for accessibility.
+ *
+ * [STANDARD] keeps the default Material 3 color scheme. [MEDIUM] uses Material 3 medium-contrast color tokens and
+ * increases message bubble opacity. [HIGH] uses Material 3 high-contrast color tokens, forces `onSurface` text in
+ * message bubbles, and replaces translucent node-color fills with opaque theme surfaces plus accent borders.
+ */
+enum class ContrastLevel(val value: Int) {
+    STANDARD(0),
+    MEDIUM(1),
+    HIGH(2),
+    ;
+
+    companion object {
+        fun fromValue(value: Int): ContrastLevel = entries.firstOrNull { it.value == value } ?: STANDARD
+    }
+}
+
+/**
+ * Composition local providing the current [ContrastLevel].
+ *
+ * Read by components that need to adapt their rendering for accessibility (e.g. message bubbles, signal indicators).
+ */
+val LocalContrastLevel = staticCompositionLocalOf { ContrastLevel.STANDARD }

core/ui/src/commonMain/kotlin/org/meshtastic/core/ui/theme/Theme.kt

@@ -14,7 +14,7 @@
  * You should have received a copy of the GNU General Public License
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
-@file:Suppress("UnusedPrivateProperty")
+@file:Suppress("MatchingDeclarationName")
 
 package org.meshtastic.core.ui.theme
 
@@ -25,6 +25,7 @@ import androidx.compose.material3.MotionScheme.Companion.expressive
 import androidx.compose.material3.darkColorScheme
 import androidx.compose.material3.lightColorScheme
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.CompositionLocalProvider
 import androidx.compose.runtime.Immutable
 import androidx.compose.ui.graphics.Color
 
@@ -272,19 +273,33 @@ val unspecified_scheme = ColorFamily(Color.Unspecified, Color.Unspecified, Color
 fun AppTheme(
     darkTheme: Boolean = isSystemInDarkTheme(),
     dynamicColor: Boolean = true,
+    contrastLevel: ContrastLevel = ContrastLevel.STANDARD,
     content:
     @Composable()
     () -> Unit,
 ) {
-    val dynamicScheme = if (dynamicColor) dynamicColorScheme(darkTheme) else null
-    val colorScheme = dynamicScheme ?: if (darkTheme) darkScheme else lightScheme
+    val dynamicScheme =
+        if (dynamicColor && contrastLevel == ContrastLevel.STANDARD) {
+            dynamicColorScheme(darkTheme)
+        } else {
+            null
+        }
+    val colorScheme =
+        dynamicScheme
+            ?: when (contrastLevel) {
+                ContrastLevel.MEDIUM -> if (darkTheme) mediumContrastDarkColorScheme else mediumContrastLightColorScheme
+                ContrastLevel.HIGH -> if (darkTheme) highContrastDarkColorScheme else highContrastLightColorScheme
+                else -> if (darkTheme) darkScheme else lightScheme
+            }
 
-    MaterialExpressiveTheme(
-        colorScheme = colorScheme,
-        typography = AppTypography,
-        motionScheme = expressive(),
-        content = content,
-    )
+    CompositionLocalProvider(LocalContrastLevel provides contrastLevel) {
+        MaterialExpressiveTheme(
+            colorScheme = colorScheme,
+            typography = AppTypography,
+            motionScheme = expressive(),
+            content = content,
+        )
+    }
 }
 
 const val MODE_DYNAMIC = 6969420

core/ui/src/commonMain/kotlin/org/meshtastic/core/ui/viewmodel/UIViewModel.kt

@@ -118,6 +118,7 @@ class UIViewModel(
     }
 
     val theme: StateFlow<Int> = uiPrefs.theme
+    val contrastLevel: StateFlow<Int> = uiPrefs.contrastLevel
 
     val firmwareEdition = meshLogRepository.getMyNodeInfo().map { nodeInfo -> nodeInfo?.firmware_edition }