M7: polish + E2E + docs (layout pass, theming, states, e2e driver, schema, setup.md, security)

app/shared/build.gradle.kts

@@ -35,6 +35,9 @@ kotlin {
         }
         // M4: ExoPlayer (Media3) for inline audio/video playback (Android only).
         androidMain.dependencies {
+            // M7: EncryptedSharedPreferences for the pairing token
+            // (docs/09 §9.7; AndroidSecureStore).
+            implementation("androidx.security:security-crypto:1.1.0")
             implementation("androidx.media3:media3-exoplayer:1.3.1")
             implementation("androidx.media3:media3-ui:1.3.1")
             // SAF picker (rememberLauncherForActivityResult).