fix: remove $uri/ from nginx try_files to prevent /guide directory redirect (refs #203)

The /guide SPA route conflicts with the static /guide/ screenshot directory.
Nginx's try_files $uri/ matches the directory and issues a 301 redirect to
/guide/ with trailing slash, bypassing SPA routing. Removing $uri/ ensures
all non-file paths fall through to index.html for client-side routing.

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

frontend/nginx.conf

@@ -19,7 +19,7 @@ http {
         
         # Handle client-side routing
         location / {
-            try_files $uri $uri/ /index.html;
+            try_files $uri /index.html;
         }
         
         # Enable gzip compression