Use new KMP project structure on generated projects

[alexstyl]

Summary

• migrate generated projects to the JetBrains-style module layout with shared, androidApp, iosApp, desktopApp, and webApp
• keep web generation wasm-only and move the launcher/build wiring into webApp
• update target-add flows so JVM, iOS, and Wasm align with the split module structure instead of mutating the shared module into an app module
• simplify template rendering in Cli.kt by centralizing shared placeholder expansion and Wasm preload task generation
• migrate generated previews to androidx.compose.ui.tooling.preview.Preview with org.jetbrains.compose.ui:ui-tooling-preview
• replace deprecated generated Android KMP and Compose web wiring with android {} plus direct version-catalog Compose UI dependencies
• stop forcing compileIosMainKotlinMetadata during project creation so generation stays clean even when upstream native dependency metadata emits duplicate-KLIB warnings

Verification

• ./gradlew test spotlessCheck
• ./gradlew run --args='create-app /tmp/composables-cli-preview4 --package=com.example.preview --app-name=Preview --targets=jvm,android,ios,wasm --overwrite'
• generated project: ./gradlew :androidApp:assembleDebug
• generated project: ./gradlew :webApp:wasmJsBrowserDistribution

Notes

• The generated shared module now uses androidx.compose.ui.tooling.preview.Preview, org.jetbrains.compose.ui:ui-tooling-preview, androidRuntimeClasspath(org.jetbrains.compose.ui:ui-tooling), and the new android {} Kotlin Multiplatform Android DSL.
• Manual compileIosMainKotlinMetadata still reports duplicate KLIB unique_name warnings from the native metadata dependency graph behind com.composables:ui; the generator no longer triggers that task during creation.
• The Wasm distribution task is clean from generator-owned deprecations; the remaining output is upstream tooling noise such as Gradle configuration-time npm resolution warnings and Node's url.parse() deprecation warning during npm install.