feat(setup): bootstrap Android plugin and web UI

This initial commit adds a multi-part scaffold for Wechselbild, including a web UI and an Android plugin.
It introduces frontend assets and a package.json-based dev setup, plus plugin scaffolding for Android with Kotlin sources and Cargo.toml for the Tauri plugin.

- Adds Android wallpaper plugin with Kotlin sources and manifest
- Includes web UI scaffold with index.html and package.json
- Adds Tauri plugin scaffold with Cargo.toml and build config

src-tauri/gen/android/gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,6 @@
+#Tue May 10 19:22:52 CST 2022
+distributionBase=GRADLE_USER_HOME
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.14.3-bin.zip
+distributionPath=wrapper/dists
+zipStorePath=wrapper/dists
+zipStoreBase=GRADLE_USER_HOME