fix(android): restore tauri::Emitter import for Docker builder toolchain

Edition 2024 on local macOS auto-resolves the Emitter trait, but the
Docker builder's Rust/Tauri version requires the explicit import for
AppHandle::emit() to resolve. Keeps the warning locally to avoid
breaking the CI build.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

desktop/src-tauri/src/engine.rs

@@ -12,6 +12,7 @@ use std::net::SocketAddr;
 use std::sync::atomic::{AtomicBool, AtomicU8, AtomicU32, AtomicU64, Ordering};
 use std::sync::Arc;
 use std::time::Instant;
+use tauri::Emitter;
 use tokio::sync::Mutex;
 use tracing::{error, info};