feat(immich): add Immich self-hosted import support

Adds an ImmichClient for Android to connect to a self-hosted Immich
server, fetch albums and assets, and import selected images locally.
API keys are encrypted with Android Keystore and stored securely.
The plugin now exposes connect, disconnect and import actions and
is documented for Immich import usage.

- Encrypted Immich API keys with Android Keystore
- Exposed connect, disconnect and import actions in the plugin
- Updated docs and metadata to reflect Immich import flow

src-tauri/gen/android/app/build.gradle.kts

@@ -17,7 +17,9 @@ android {
     compileSdk = 36
     namespace = "de.wechselbild.app"
     defaultConfig {
-        manifestPlaceholders["usesCleartextTraffic"] = "false"
+        // Immich is frequently hosted on a private LAN without TLS. The app only
+        // connects to the server URL explicitly entered by the user.
+        manifestPlaceholders["usesCleartextTraffic"] = "true"
         applicationId = "de.wechselbild.app"
         minSdk = 24
         targetSdk = 36
@@ -68,4 +70,4 @@ dependencies {
     androidTestImplementation("androidx.test.espresso:espresso-core:3.5.0")
 }
 
-apply(from = "tauri.build.gradle.kts")
+apply(from = "tauri.build.gradle.kts")