feat: add MockK dependency and update README documentation for diagnostic features

app/build.gradle.kts

@@ -73,6 +73,7 @@ dependencies {
   // Local tests: jUnit, coroutines, Android runner
   testImplementation(libs.junit)
   testImplementation(libs.kotlinx.coroutines.test)
+  testImplementation(libs.mockk)
 
   // Instrumented tests: jUnit rules and runners
   androidTestImplementation(libs.androidx.test.core)

app/src/main/java/com/example/esp32aldldashboard/ui/charts/ChartsScreen.kt

@@ -1,5 +1,7 @@
+@file:OptIn(androidx.compose.material3.ExperimentalMaterial3Api::class)
 package com.example.esp32aldldashboard.ui.charts
 
+import androidx.compose.material3.ExperimentalMaterial3Api
 import androidx.compose.foundation.Canvas
 import androidx.compose.foundation.layout.*
 import androidx.compose.foundation.lazy.LazyRow