chore: get Android project building (toolchain, deps, manifest, launcher icon)

- Fix dependency versions (Retrofit 2.11, OkHttp 4.12, Compose BOM)
- Add Material Components for the app theme
- Add --add-exports/--add-opens for kapt on JDK 21
- Remove deprecated manifest package attr; add INTERNET permission
- Add adaptive launcher icon

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/src/main/java/com/scarriffle/calendarr/MainActivity.kt

@@ -0,0 +1,30 @@
+package com.scarriffle.calendarr
+
+import android.os.Bundle
+import androidx.activity.ComponentActivity
+import androidx.activity.compose.setContent
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Surface
+import androidx.compose.material3.Text
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import com.scarriffle.calendarr.ui.theme.CalendarrTheme
+import dagger.hilt.android.AndroidEntryPoint
+
+@AndroidEntryPoint
+class MainActivity : ComponentActivity() {
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        setContent {
+            CalendarrTheme {
+                Surface(modifier = Modifier.fillMaxSize(), color = MaterialTheme.colorScheme.background) {
+                    Box(contentAlignment = Alignment.Center, modifier = Modifier.fillMaxSize()) {
+                        Text(text = "Calendarr Android", style = MaterialTheme.typography.headlineMedium)
+                    }
+                }
+            }
+        }
+    }
+}