fix(#100): hide action button labels on mobile to prevent toolbar overflow

At 320px, showing "Annotieren" + "Bearbeiten" + download pushed the
toolbar past its bounds. Icon-only at mobile, labels revealed at sm:.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/components/DocumentTopBar.svelte

@@ -58,7 +58,7 @@ const compactMeta = $derived.by(() => {
 </script>
 
 <div
-	class="z-20 flex shrink-0 items-center justify-between border-b border-line bg-surface px-6 py-3 shadow-sm"
+	class="z-20 flex shrink-0 items-center justify-between border-b border-line bg-surface px-3 py-3 shadow-sm sm:px-6"
 	data-topbar
 >
 	<!-- Left: back + title -->
@@ -111,13 +111,16 @@ const compactMeta = $derived.by(() => {
 					aria-hidden="true"
 					class="h-4 w-4 {annotateMode ? 'invert' : ''}"
 				/>
-				{annotateMode ? m.doc_panel_annotate_stop() : m.doc_panel_annotate()}
+				<span class="hidden sm:inline"
+					>{annotateMode ? m.doc_panel_annotate_stop() : m.doc_panel_annotate()}</span
+				>
 			</button>
 		{/if}
 
 		{#if canWrite}
 			<a
 				href="/documents/{doc.id}/edit"
+				aria-label={m.btn_edit()}
 				class="flex items-center gap-2 rounded border border-primary bg-transparent px-3 py-1.5 text-xs font-medium text-ink transition hover:bg-primary hover:text-primary-fg"
 			>
 				<img
@@ -126,7 +129,7 @@ const compactMeta = $derived.by(() => {
 					aria-hidden="true"
 					class="h-4 w-4"
 				/>
-				{m.btn_edit()}
+				<span class="hidden sm:inline">{m.btn_edit()}</span>
 			</a>
 		{/if}