fix: shrink navbar brand to 1rem on mobile so full 'mc-webui' fits

At 1.25rem the brand was still ~120px wide and got truncated to
'mc-we...' on a 360px-wide S20. Drop to 1rem so the whole name
fits without ellipsis while the navbar stays on one row.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

app/static/css/style.css

@@ -565,7 +565,7 @@ main {
 
     /* Navbar: Shrink brand title and let it truncate if needed */
     .navbar-brand.h1 {
-        font-size: 1.25rem;
+        font-size: 1rem;
         min-width: 0;
         overflow: hidden;
         text-overflow: ellipsis;