style: apply cargo fmt formatting to existing codebase

Run `cargo fmt` across all Rust source files to enforce consistent
formatting (import ordering, line wrapping, match arm braces).

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

src/interfaces/api/handlers/favorites_handler.rs

@@ -1,4 +1,9 @@
-use axum::{Json, extract::{Path, State}, http::StatusCode, response::IntoResponse};
+use axum::{
+    Json,
+    extract::{Path, State},
+    http::StatusCode,
+    response::IntoResponse,
+};
 use serde::Deserialize;
 use std::sync::Arc;
 use tracing::{error, info};