feat(bulk-upload): add UploadSaveBar component + fix bulk_save_cta message

Save bar with sticky positioning, a determinate progress bar while
uploading chunks, plural save CTA, and a destructive discard link.
Replaces broken ICU plural in bulk_save_cta with two-key approach
(bulk_save_cta_one / bulk_save_cta) since Paraglide 2.5 does not support
ICU plural syntax.

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

frontend/src/lib/components/document/UploadSaveBar.svelte

@@ -0,0 +1,39 @@
+<script lang="ts">
+import * as m from '$lib/paraglide/messages';
+
+let {
+	fileCount,
+	chunkProgress,
+	onSave,
+	onDiscard
+}: {
+	fileCount: number;
+	chunkProgress?: { done: number; total: number };
+	onSave: () => void;
+	onDiscard: () => void;
+} = $props();
+</script>
+
+<div
+	class="border-brand-sand sticky bottom-0 z-10 -mx-4 border-t bg-white px-6 py-4 shadow-[0_-2px_8px_rgba(0,0,0,0.06)]"
+>
+	{#if chunkProgress}
+		<progress
+			value={chunkProgress.done}
+			max={chunkProgress.total}
+			class="[&::-webkit-progress-bar]:bg-brand-sand mb-3 h-1 w-full rounded-full [&::-webkit-progress-bar]:rounded-full [&::-webkit-progress-value]:rounded-full [&::-webkit-progress-value]:bg-brand-mint"
+		></progress>
+	{/if}
+	<div class="flex items-center justify-between">
+		<button type="button" onclick={onDiscard} class="text-sm text-red-600/70 hover:text-red-700">
+			{m.bulk_discard_all()}
+		</button>
+		<button
+			type="button"
+			onclick={onSave}
+			class="min-h-[44px] rounded-sm bg-brand-navy px-6 text-sm font-bold tracking-widest text-white uppercase hover:bg-brand-navy/90"
+		>
+			{fileCount === 1 ? 'Speichern →' : `${fileCount} speichern →`}
+		</button>
+	</div>
+</div>