feat(web): keyboard reorder on playlist tracks (Tier C10)

Drag was already wired via @neodrag/svelte; this adds the missing
keyboard path so reorder is accessible without a pointer device.

- The drag handle becomes a real <button> (focusable). Disabled
  when canDrag is false so non-owners + unavailable tracks can't
  attempt a move.
- ArrowUp / ArrowDown on the focused handle call
  onMove(row.position, row.position +/- 1). Bounds clamping
  already lives in the page-level handler (playlists/[id]/+page.svelte:39),
  so out-of-range targets resolve as no-ops.
- Matches QueueTrackRow's pattern: aria-label "Reorder track …",
  aria-keyshortcuts, swallow Space/Enter to avoid scrolling.

Test updates: drag-handle assertions retargeted to /reorder track/
+ two new ArrowUp/ArrowDown handler tests.

web/src/lib/components/PlaylistTrackRow.test.ts

@@ -67,26 +67,46 @@ describe('PlaylistTrackRow', () => {
     expect(screen.getByText('2:17')).toBeInTheDocument();
   });
 
-  test('shows drag handle and remove button for owner', () => {
+  test('shows reorder handle and remove button for owner', () => {
     render(PlaylistTrackRow, {
       props: { row: live, isOwner: true, onRemove: vi.fn(), onPlay: vi.fn() }
     });
-    expect(screen.getByLabelText('Drag handle')).toBeInTheDocument();
+    expect(screen.getByLabelText(/reorder track/i)).toBeInTheDocument();
     expect(
       screen.getByLabelText(/Remove Roygbiv from playlist/i)
     ).toBeInTheDocument();
   });
 
-  test('hides drag handle and remove button for non-owner', () => {
+  test('hides reorder handle and remove button for non-owner', () => {
     render(PlaylistTrackRow, {
       props: { row: live, isOwner: false, onRemove: vi.fn(), onPlay: vi.fn() }
     });
-    expect(screen.queryByLabelText('Drag handle')).not.toBeInTheDocument();
+    expect(screen.queryByLabelText(/reorder track/i)).not.toBeInTheDocument();
     expect(
       screen.queryByLabelText(/Remove Roygbiv from playlist/i)
     ).not.toBeInTheDocument();
   });
 
+  test('ArrowDown on the reorder handle calls onMove(pos, pos+1)', async () => {
+    const onMove = vi.fn();
+    render(PlaylistTrackRow, {
+      props: { row: live, isOwner: true, onRemove: vi.fn(), onPlay: vi.fn(), onMove }
+    });
+    const handle = screen.getByLabelText(/reorder track/i);
+    await fireEvent.keyDown(handle, { key: 'ArrowDown' });
+    expect(onMove).toHaveBeenCalledWith(2, 3);
+  });
+
+  test('ArrowUp on the reorder handle calls onMove(pos, pos-1)', async () => {
+    const onMove = vi.fn();
+    render(PlaylistTrackRow, {
+      props: { row: live, isOwner: true, onRemove: vi.fn(), onPlay: vi.fn(), onMove }
+    });
+    const handle = screen.getByLabelText(/reorder track/i);
+    await fireEvent.keyDown(handle, { key: 'ArrowUp' });
+    expect(onMove).toHaveBeenCalledWith(2, 1);
+  });
+
   test('greyed-out + strikethrough when track_id is null', () => {
     render(PlaylistTrackRow, {
       props: { row: removed, isOwner: true, onRemove: vi.fn(), onPlay: vi.fn() }