Fix highlight class collision with the lookup mode row

The prototype's .seg (display:flex segment control) clobbered the new
highlight segments, turning every rhyme span into a full-width bar.
Highlight segments are .hseg now.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

static/index.html

@@ -115,7 +115,7 @@
      underline; both can overlap in different colors. Background/shadow
      only, so the textarea text on top stays crisp and box metrics stay
      identical (no horizontal padding!) */
-  .seg { border-radius: 4px; }
+  .hseg { border-radius: 4px; }
   .offbeat {
     text-decoration: underline wavy color-mix(in srgb, var(--r6) 45%, transparent);
     text-decoration-skip-ink: none;
@@ -508,7 +508,7 @@ function render(){
              : `color-mix(in srgb, ${colorOf(p)} 55%, transparent)`;
         }
         if(ul) style += `box-shadow:inset 0 -2px 0 0 ${ul};`;
-        h += `<span class="seg" style="${style}">${text}</span>`;
+        h += `<span class="hseg" style="${style}">${text}</span>`;
       }
     }
     const m = fresh && analysis.meter ? analysis.meter.find(x=>x.l===i) : null;