math tracker: pass string classes to lucide icons (fixes owner-view 500)

src/routes/trackers/math/+page.svelte

@@ -376,7 +376,7 @@
 							<span class="ptitle">{p.title}</span>
 							<span class="pbar">{@render bar(p.counts, p.chapters.length)}</span>
 							<span class="muted pcount">{p.counts.done}/{p.chapters.length}</span>
-							<ChevronDown size={16} class={['chev', { flipped: !collapsedParts[p.key] }]} />
+							<ChevronDown size={16} class={!collapsedParts[p.key] ? 'chev flipped' : 'chev'} />
 						</button>
 						{#if !collapsedParts[p.key]}
 							<ul class="chapters">
@@ -408,7 +408,7 @@
 													>
 												{/if}
 											</span>
-											<ChevronDown size={14} class={['chev', { flipped: open[c.key] }]} />
+											<ChevronDown size={14} class={open[c.key] ? 'chev flipped' : 'chev'} />
 										</button>
 										{#if open[c.key]}{@render details(c)}{/if}
 									</li>