refactor(history): reuse IconButton; drop redundant emptyText overrides

The HistoryList clear button hand-rolled the same `.icon-btn danger`
styles that were extracted into the shared IconButton component one
commit earlier — the exact duplication that refactor targeted. Swap it
for <IconButton variant="danger">; data-testid/aria pass through the
component's {...rest} spread so behaviour is unchanged.

Both callers also passed an emptyText equal to the prop's default; drop
the overrides so the default lives in one place.

No behaviour change, so no version bump.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/routes/library/+page.svelte

@@ -95,12 +95,7 @@
         initialDistinct={data.distinctPageTags}
     />
 {:else}
-    <HistoryList
-        entries={data.history}
-        onClear={clearOne}
-        emptyText="Nothing here yet — open any manga and a row will land here once you turn a page."
-        testid="library-history"
-    />
+    <HistoryList entries={data.history} onClear={clearOne} testid="library-history" />
 {/if}
 
 <style>