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

plugins/android/settings.gradle

@@ -0,0 +1,31 @@
+pluginManagement {
+    repositories {
+        mavenCentral()
+        gradlePluginPortal()
+        google()
+    }
+    resolutionStrategy {
+        eachPlugin {
+            switch (requested.id.id) {
+                case "com.android.library":
+                    useVersion("8.0.2")
+                    break
+                case "org.jetbrains.kotlin.android":
+                    useVersion("1.8.20")
+                    break
+            }
+        }
+    }
+}
+
+dependencyResolutionManagement {
+    repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS)
+    repositories {
+        mavenCentral()
+        google()
+
+    }
+}
+
+include ':tauri-android'
+project(':tauri-android').projectDir = new File('./.tauri/tauri-api')