refactor(logging): use Timber instead of Kermit

Android-only project, so Timber (the de-facto Android logging lib) fits better than the
KMP-oriented Kermit.

- Catalog: kermit -> timber (com.jakewharton.timber:timber 5.0.1).
- core:data: Ktor Logging bridged to Timber; safeCall logs via Timber.
- app: plant Timber.DebugTree() in debug only (buildConfig enabled for BuildConfig.DEBUG).

app/build.gradle.kts

@@ -4,6 +4,13 @@ plugins {
     alias(libs.plugins.architecture.koin)
 }
 
+android {
+    // Needed for BuildConfig.DEBUG (gating the Timber DebugTree).
+    buildFeatures {
+        buildConfig = true
+    }
+}
+
 dependencies {
     // :app is the only place modules are assembled and the dependency graph is wired.
     implementation(project(":core:data"))
@@ -15,6 +22,8 @@ dependencies {
     implementation(libs.bundles.lifecycle.compose)
     // Material Components — required for the Material3 XML Activity theme.
     implementation(libs.material)
+    // Logging — the DebugTree is planted here; other modules log via Timber's static API.
+    implementation(libs.timber)
 
     androidTestImplementation(libs.androidx.compose.ui.test.junit4)
     debugImplementation(libs.androidx.compose.ui.test.manifest)