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/ui/theme/Color.kt

@@ -0,0 +1,13 @@
+package com.scarriffle.calendarr.ui.theme
+
+import androidx.compose.ui.graphics.Color
+
+val md_theme_light_primary = Color(0xFF4285F4)
+val md_theme_light_onPrimary = Color(0xFFFFFFFF)
+val md_theme_light_background = Color(0xFFFFFFFF)
+val md_theme_light_onBackground = Color(0xFF000000)
+
+val md_theme_dark_primary = Color(0xFF8AB4F8)
+val md_theme_dark_onPrimary = Color(0xFF000000)
+val md_theme_dark_background = Color(0xFF000000)
+val md_theme_dark_onBackground = Color(0xFFFFFFFF)

app/src/main/java/com/scarriffle/calendarr/ui/theme/Theme.kt

@@ -0,0 +1,35 @@
+package com.scarriffle.calendarr.ui.theme
+
+import androidx.compose.foundation.isSystemInDarkTheme
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.darkColorScheme
+import androidx.compose.material3.lightColorScheme
+import androidx.compose.runtime.Composable
+
+private val LightColors = lightColorScheme(
+    primary = md_theme_light_primary,
+    onPrimary = md_theme_light_onPrimary,
+    background = md_theme_light_background,
+    onBackground = md_theme_light_onBackground,
+)
+
+private val DarkColors = darkColorScheme(
+    primary = md_theme_dark_primary,
+    onPrimary = md_theme_dark_onPrimary,
+    background = md_theme_dark_background,
+    onBackground = md_theme_dark_onBackground,
+)
+
+@Composable
+fun CalendarrTheme(
+    darkTheme: Boolean = isSystemInDarkTheme(),
+    content: @Composable () -> Unit,
+) {
+    val colors = if (darkTheme) DarkColors else LightColors
+
+    MaterialTheme(
+        colorScheme = colors,
+        typography = androidx.compose.material3.Typography(),
+        content = content,
+    )
+}