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).

build.gradle.kts

@@ -3,9 +3,9 @@ plugins {
     alias(libs.plugins.android.application) apply false
     alias(libs.plugins.android.library) apply false
     alias(libs.plugins.kotlin.android) apply false
-    alias(libs.plugins.kotlin.multiplatform) apply false
     alias(libs.plugins.kotlin.compose) apply false
-    alias(libs.plugins.compose.multiplatform) apply false
+    alias(libs.plugins.kotlin.serialization) apply false
+    alias(libs.plugins.kotlin.ksp) apply false
     alias(libs.plugins.kover) apply false
 }
 
@@ -14,6 +14,21 @@ val test by tasks.registering {
     description = "Runs available unit tests for the included projects."
 }
 
+subprojects {
+    val rootTest = rootProject.tasks.named("test")
+    tasks.matching {
+        it.name == "allTests" ||
+            it.name.endsWith("DebugUnitTest")
+    }.configureEach {
+        rootTest.configure {
+            dependsOn(this@configureEach)
+        }
+    }
+    tasks.withType<Test>().configureEach {
+        maxHeapSize = "4g"
+    }
+}
+
 allprojects {
     configurations.all {
         resolutionStrategy {
@@ -24,19 +39,3 @@ allprojects {
         }
     }
 }
-
-subprojects {
-    val rootTest = rootProject.tasks.named("test")
-    tasks.matching {
-        it.name == "allTests" ||
-            it.name == "desktopTest" ||
-            it.name.endsWith("DebugUnitTest")
-    }.configureEach {
-        rootTest.configure {
-            dependsOn(this@configureEach)
-        }
-    }
-    tasks.withType<Test>().configureEach {
-        maxHeapSize = "4g"
-    }
-}