fix: stabilize waveform seekbar width when player time changes

Add min-width to .player-time elements so they don't resize when the
displayed time string changes length (e.g. "9:59" → "10:00"). Not all
fonts support the tabular-nums font-variant, so without a min-width the
time elements can change size and cause the waveform seekbar to
continuously resize as playback progresses.

Also align the elapsed time to the right and duration to the left so
they sit flush against the waveform edges.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/styles/layout.css

@@ -632,6 +632,15 @@
   font-variant-numeric: tabular-nums;
   white-space: nowrap;
   flex-shrink: 0;
+  min-width: 2.5rem;
+}
+
+.player-time:first-child {
+  text-align: right;
+}
+
+.player-time:last-child {
+  text-align: left;
 }
 
 /* Volume section */