Fix rust-embed: correct folder path and remove duplicate feature

- Fix RustEmbed folder path to use $CARGO_MANIFEST_DIR/ui
- Remove duplicate interpolate-folder-path feature (now in workspace)
- Verified: 13 HTML files embedded, binary works from any directory

src/ui_server/mod.rs

@@ -25,7 +25,7 @@ use tower_http::services::{ServeDir, ServeFile};
 
 #[cfg(feature = "embed-ui")]
 #[derive(RustEmbed)]
-#[folder = "ui"]
+#[folder = "$CARGO_MANIFEST_DIR/ui"]
 struct Assets;
 
 use crate::shared::AppState;