feat(build): KMP → Android-only migration (Phase 1.2)

- Delete desktopApp/ and shared/ modules.
- Merge shared commonMain + androidMain + readerJvmMain sources into app/src/main/kotlin.
- Resolve expect/actual declarations by keeping android implementations.
- Remove project(':shared') dependency and KMP plugins from build files.
- Simplify settings.gradle.kts to single :app module; root project renamed BookReader.
- Remove JVM-only code (javax.imageio/ImageIO in SharedJvmBookLoader).
- Make LocalFolderSync helpers public for cross-package use in Android module.
- Baseline ':app:assembleOssDebug' passes (APK ~80 MB).

settings.gradle.kts

@@ -1,12 +1,6 @@
 pluginManagement {
     repositories {
-        google {
-            content {
-                includeGroupByRegex("com\\.android.*")
-                includeGroupByRegex("com\\.google.*")
-                includeGroupByRegex("androidx.*")
-            }
-        }
+        google()
         mavenCentral()
         gradlePluginPortal()
     }
@@ -18,25 +12,9 @@ dependencyResolutionManagement {
         mavenCentral()
         maven("https://jitpack.io")
         maven("https://jogamp.org/deployment/maven")
-        maven("https://jitpack.io")
     }
 }
 
-rootProject.name = "Reader"
+rootProject.name = "BookReader"
 
-fun isDesktopOnlyBuild(): Boolean {
-    providers.gradleProperty("desktopOnly").orNull
-        ?.let { return it.equals("true", ignoreCase = true) }
-
-    val requestedTasks = gradle.startParameter.taskNames
-    return requestedTasks.isNotEmpty() && requestedTasks.all { taskName ->
-        val normalized = taskName.removePrefix(":")
-        normalized.startsWith("desktopApp:")
-    }
-}
-
-if (!isDesktopOnlyBuild()) {
-    include(":app")
-}
-include(":shared")
-include(":desktopApp")
+include(":app")