feat(ui): show total track length on progress bar instead of remaining

Right-hand time on the playback bar now displays the full track length
(e.g. 1:00:00) rather than the countdown (-49:39). Updated the progress-bar
click-to-seek handler to read total directly from that label instead of
deriving it from current + remaining. The canvas remaining-time display
mode is untouched.

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

web/static/app.js

@@ -181,11 +181,11 @@ function applyStatus(st) {
     currentLength   = st.length;
     progressFill.style.width = (st.position / st.length * 100).toFixed(1) + '%';
     timeCurrent.textContent  = fmtTime(st.position);
-    timeLength.textContent   = '-' + fmtTime(st.length - st.position);
+    timeLength.textContent   = fmtTime(st.length);   // total track length
   } else {
     progressFill.style.width = '0%';
     timeCurrent.textContent  = '0:00';
-    timeLength.textContent   = '-0:00';
+    timeLength.textContent   = '0:00';
   }
 
   btnPlay.textContent = st.state === 'playing' ? SYM.pause : SYM.play;
@@ -215,9 +215,8 @@ qsa('.btn-seek').forEach(function(btn) {
 });
 
 $('progress-bar').addEventListener('click', function(e) {
-  var current   = parseTime(timeCurrent.textContent);
-  var remaining = parseTime(timeLength.textContent.replace('-', ''));
-  var total     = current + remaining;
+  var current = parseTime(timeCurrent.textContent);
+  var total   = parseTime(timeLength.textContent);   // right value is now total length
   if (!total) return;
   var rect   = e.currentTarget.getBoundingClientRect();
   var target = Math.round((e.clientX - rect.left) / rect.width * total);