Audit 9b: Dynamic color (Material You) + 48dp min touch target helpers

Dynamic color opt-in on Android 12+ via expect/actual DynamicColor:
- commonMain: expect isDynamicColorSupported() + rememberDynamicColorScheme()
- androidMain: SDK>=31 gate, dynamicLight/DarkColorScheme(context)
- iOS/JVM/JS/WASM: no-op actuals
- ThemeManager gains useDynamicColor StateFlow, persisted via ThemeStorage
- App.kt wires both currentTheme + useDynamicColor into HoneyDueTheme
- ThemeSelectionScreen exposes the "Use system colors" toggle

Touch target helpers:
- Modifier.minTouchTarget(48.dp) + Modifier.clickableWithRipple
- Applied at audit-flagged sites in CompleteTaskScreen

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

composeApp/src/commonMain/kotlin/com/tt/honeyDue/App.kt

@@ -151,8 +151,9 @@ fun App(
     }
 
     val currentTheme by remember { derivedStateOf { ThemeManager.currentTheme } }
+    val useDynamicColor by remember { derivedStateOf { ThemeManager.useDynamicColor } }
 
-    HoneyDueTheme(themeColors = currentTheme) {
+    HoneyDueTheme(themeColors = currentTheme, useDynamicColor = useDynamicColor) {
         // Handle contractor file imports (Android-specific, no-op on other platforms)
         ContractorImportHandler(
             pendingContractorImportUri = pendingContractorImportUri,