fix: add TraceLayer and Vite proxy config (supporting changes)

- Add tower-http TraceLayer to Axum router for request logging
- Configure Vite dev server proxy for /api and /media to localhost:3000
- Add TEST_GUIDE.md for manual frontend testing steps

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/main.rs

@@ -3,6 +3,7 @@ use axum::extract::DefaultBodyLimit;
 use axum::routing::{delete, get, patch, post};
 use axum::Router;
 use tower_http::services::ServeDir;
+use tower_http::trace::TraceLayer;
 use tracing_subscriber::{layer::SubscriberExt, util::SubscriberInitExt};
 
 mod auth;
@@ -91,6 +92,7 @@ async fn main() -> Result<()> {
         .route("/health", get(|| async { "ok" }))
         .merge(api)
         .nest_service("/media", media_service)
+        .layer(TraceLayer::new_for_http())
         .with_state(state);
 
     let listener = tokio::net::TcpListener::bind(("0.0.0.0", config.app_port)).await?;