Add Kotlin Multiplatform mobile client

A Compose Multiplatform app (mobile/) targeting Android, iOS, and desktop,
sharing one Kotlin codebase: OIDC login via PKCE against the same Zitadel
instance the web player uses (loopback redirect on desktop, a musify://
custom scheme on mobile), a token store per platform, and a first pass at
browsing/streaming tracks through the existing API.

deploy/compose.yml's zitadel-init gains a third OIDC app registration
("Musify Native", public client, no secret) alongside the existing API and
web apps, writing its client id to NATIVE_CLIENT_ID in the env file the same
way the other two already do.

mobile/gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,7 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.14.5-bin.zip
+networkTimeout=10000
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists