Fix subtitle size and don't auto-select any track on load

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

frontend/src/index.css

@@ -21,8 +21,8 @@ video::cue {
   text-align: center;
   background: rgba(0, 0, 0, 0.75);
   color: #ffffff;
-  font-size: 1rem;
-  line-height: 1.4;
+  font-size: 1.4rem;
+  line-height: 1.5;
 }
 
 @layer utilities {

frontend/src/pages/Watch.jsx

@@ -906,14 +906,13 @@ export default function Watch() {
                   v.play().catch(() => {});
                 }}
               >
-                {subtitleFiles.map((s, i) => (
+                {subtitleFiles.map((s) => (
                   <track
                     key={s.lang}
                     kind="subtitles"
                     src={s.url}
                     srcLang={s.lang}
                     label={s.lang}
-                    default={i === 0}
                   />
                 ))}
               </video>