Use the real institutional logo for the header wordmark, not plain text

The header link was just styled "UHHM" text, unrelated to the actual
brand mark - swapped in the institutional logo (the three-arch
"building" mark, matching infrastructure/assets/brand/institutional-*.svg
and Gitea's own homepage logo) instead. Dark-stroke variant only -
portal is a single permanent dark theme, no light mode to switch for.
Same explicit-route treatment the favicon files needed (the /*any
wildcard route would otherwise swallow the request before the static
file handler gets a chance).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/main.rs

@@ -119,6 +119,7 @@ async fn main() -> anyhow::Result<()> {
     );
     let favicon_light_path = format!("{}/favicon-light.svg", leptos_options.site_root);
     let favicon_dark_path = format!("{}/favicon-dark.svg", leptos_options.site_root);
+    let wordmark_path = format!("{}/wordmark.svg", leptos_options.site_root);
     let fonts_dir = format!("{}/fonts", leptos_options.site_root);
 
     let app = Router::new()
@@ -133,6 +134,7 @@ async fn main() -> anyhow::Result<()> {
         .nest_service("/fonts", ServeDir::new(fonts_dir))
         .route_service("/favicon-light.svg", ServeFile::new(favicon_light_path))
         .route_service("/favicon-dark.svg", ServeFile::new(favicon_dark_path))
+        .route_service("/wordmark.svg", ServeFile::new(wordmark_path))
         .leptos_routes_with_context(
             &state,
             routes,