feat(android): slim NowPlaying scrubber — 4dp track + tight slider

The M3 Slider default track is 16dp tall and the Slider itself
expands to the 48dp interactive-component minimum, so the 14dp
thumb we'd already shrunk to a flat circle was still sitting in
the middle of a fat horizontal pill with lots of empty space
above and below. Operator framing: "puffy, not a tool."

Two changes:
- Custom 4dp rounded track replaces SliderDefaults.Track. The
  thumb (14dp) now reads as visibly taller than the bar — the
  classic "handle on a string" cue that says "tool, draggable."
  Also drops M3's stop-indicator dot which the web scrubber
  doesn't have.
- Clamp the Slider's vertical footprint to 20dp via Modifier.
  height. 14dp thumb + 3dp clearance each side, vs the default
  ~17dp empty above and below. Touch area stays usable since the
  drag axis is horizontal — pulling left/right anywhere on the
  thin bar feels natural, and Slider's gesture detector still
  responds to a tap anywhere along its row.

Keeps an Android flavor (slightly thicker than the web's 2-3px
hairline; rounded caps; accent fill) without reading as bulky.

android/app/src/main/java/com/fabledsword/minstrel/player/ui/NowPlayingScreen.kt

@@ -12,6 +12,7 @@ import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.Spacer
 import androidx.compose.foundation.layout.aspectRatio
+import androidx.compose.foundation.layout.fillMaxHeight
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.height
@@ -85,6 +86,9 @@ private const val COVER_MAX_WIDTH_DP = 320
 private const val TRANSPORT_ICON_DP = 36
 private const val PLAY_PAUSE_ICON_DP = 56
 private const val POP_GRACE_MS = 500L
+private val SCRUB_TRACK_HEIGHT_DP = 4.dp
+private val SCRUB_TRACK_CORNER_DP = 2.dp
+private val SCRUB_SLIDER_HEIGHT_DP = 20.dp
 
 // Vertical drag-down threshold (in pixels) past which the gesture
 // pops the player. Matches Flutter's 80px threshold in spirit;
@@ -472,7 +476,12 @@ private fun ScrubberRow(positionMs: Long, durationMs: Long, onSeek: (Long) -> Un
         onValueChange = { newFraction ->
             if (durationMs > 0) onSeek((newFraction * durationMs).toLong())
         },
-        modifier = Modifier.fillMaxWidth(),
+        // Clamp the Slider's vertical footprint so the M3-default
+        // 48dp interactive-component padding doesn't leave the thumb
+        // floating in empty space above and below the track. 20dp =
+        // 14dp thumb + 3dp clearance each side; touch area is still
+        // wide enough since the drag axis is horizontal.
+        modifier = Modifier.fillMaxWidth().height(SCRUB_SLIDER_HEIGHT_DP),
         colors = sliderColors,
         interactionSource = interactionSource,
         // Plain filled circle to match the web client's `<input
@@ -488,6 +497,29 @@ private fun ScrubberRow(positionMs: Long, durationMs: Long, onSeek: (Long) -> Un
                     .background(accent),
             )
         },
+        // Custom 4dp rounded track. M3's default Track is 16dp tall
+        // and reads as a heavy pill rather than a measurement line;
+        // making the thumb visibly taller than the track (14dp thumb
+        // on a 4dp bar) restores the "handle on a string" cue your
+        // eye reads as "tool, draggable." Also drops M3's stop
+        // indicator dot, which the web scrubber doesn't have.
+        track = { _ ->
+            Box(modifier = Modifier.fillMaxWidth().height(SCRUB_TRACK_HEIGHT_DP)) {
+                Box(
+                    modifier = Modifier
+                        .matchParentSize()
+                        .clip(RoundedCornerShape(SCRUB_TRACK_CORNER_DP))
+                        .background(MaterialTheme.colorScheme.surfaceVariant),
+                )
+                Box(
+                    modifier = Modifier
+                        .fillMaxWidth(fraction)
+                        .fillMaxHeight()
+                        .clip(RoundedCornerShape(SCRUB_TRACK_CORNER_DP))
+                        .background(accent),
+                )
+            }
+        },
     )
     Row(
         modifier = Modifier.fillMaxWidth(),