fix: read BASE_URL from env for RSS channel link

.env.example

@@ -1,4 +1,5 @@
 DATABASE_URL=sqlite:./dev.db
+BASE_URL=http://localhost:3000
 PORT=3000
 JWT_SECRET=
 JWT_TTL_SECONDS=

crates/presentation/src/main.rs

@@ -109,7 +109,7 @@ async fn wire_dependencies() -> anyhow::Result<AppState> {
         app_ctx,
         html_renderer: Arc::new(AskamaHtmlRenderer::new()),
         rss_renderer: Arc::new(RssAdapter::new(
-            "http://localhost:3000".into(),
+            std::env::var("BASE_URL").unwrap_or_else(|_| "http://localhost:3000".into()),
         )),
     })
 }