feat: implement client-side upload queue with IndexedDB persistence

- upload-queue.ts: IndexedDB-backed queue manager using idb library
  - File blobs stored in IndexedDB (survives page reloads)
  - Sequential upload processing (one file at a time)
  - XHR-based upload with per-file progress tracking
  - Retry failed uploads, remove/clear completed items
  - Auto-resumes pending items on page load
- UploadQueue.svelte: queue progress UI component
  - Per-file: filename, size, progress bar, status badge
  - Retry button on failed items, remove button, clear completed
  - Processing indicator with pulse animation
- /upload page: file picker (multiple, image/video) with caption + hashtags
  - Drop zone UI with drag-and-drop styling
  - Caption supports inline #hashtags
  - Separate comma-separated hashtags field
  - Link to gallery feed

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

frontend/src/lib/components/UploadQueue.svelte

@@ -0,0 +1,103 @@
+<script lang="ts">
+	import { queueItems, isProcessing, retryItem, removeItem, clearCompleted } from '$lib/upload-queue';
+	import type { QueueItem } from '$lib/upload-queue';
+
+	function formatSize(bytes: number): string {
+		if (bytes < 1024) return `${bytes} B`;
+		if (bytes < 1024 * 1024) return `${(bytes / 1024).toFixed(1)} KB`;
+		return `${(bytes / (1024 * 1024)).toFixed(1)} MB`;
+	}
+
+	function statusLabel(status: QueueItem['status']): string {
+		switch (status) {
+			case 'pending': return 'Wartend';
+			case 'uploading': return 'Wird hochgeladen';
+			case 'done': return 'Fertig';
+			case 'error': return 'Fehler';
+		}
+	}
+
+	function statusColor(status: QueueItem['status']): string {
+		switch (status) {
+			case 'pending': return 'text-gray-500';
+			case 'uploading': return 'text-blue-600';
+			case 'done': return 'text-green-600';
+			case 'error': return 'text-red-600';
+		}
+	}
+
+	let items = $derived($queueItems);
+	let hasCompleted = $derived(items.some((i) => i.status === 'done'));
+</script>
+
+{#if items.length > 0}
+	<div class="mt-4 rounded-lg border border-gray-200 bg-white">
+		<div class="flex items-center justify-between border-b border-gray-100 px-4 py-3">
+			<h3 class="text-sm font-semibold text-gray-900">
+				Upload-Warteschlange
+				{#if $isProcessing}
+					<span class="ml-2 inline-block h-2 w-2 animate-pulse rounded-full bg-blue-500"></span>
+				{/if}
+			</h3>
+			{#if hasCompleted}
+				<button
+					onclick={() => clearCompleted()}
+					class="text-xs text-gray-500 hover:text-gray-700"
+				>
+					Fertige entfernen
+				</button>
+			{/if}
+		</div>
+
+		<ul class="divide-y divide-gray-100">
+			{#each items as item (item.id)}
+				<li class="px-4 py-3">
+					<div class="flex items-center justify-between">
+						<div class="min-w-0 flex-1">
+							<p class="truncate text-sm font-medium text-gray-900">{item.fileName}</p>
+							<p class="text-xs text-gray-500">{formatSize(item.fileSize)}</p>
+						</div>
+						<div class="ml-3 flex items-center gap-2">
+							<span class="text-xs font-medium {statusColor(item.status)}">
+								{statusLabel(item.status)}
+							</span>
+							{#if item.status === 'error'}
+								<button
+									onclick={() => retryItem(item.id)}
+									class="rounded bg-red-100 px-2 py-0.5 text-xs text-red-700 hover:bg-red-200"
+								>
+									Erneut
+								</button>
+							{/if}
+							{#if item.status === 'done' || item.status === 'error'}
+								<button
+									onclick={() => removeItem(item.id)}
+									class="text-gray-400 hover:text-gray-600"
+									aria-label="Entfernen"
+								>
+									<svg class="h-4 w-4" fill="none" viewBox="0 0 24 24" stroke="currentColor">
+										<path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M6 18L18 6M6 6l12 12" />
+									</svg>
+								</button>
+							{/if}
+						</div>
+					</div>
+
+					{#if item.status === 'uploading'}
+						<div class="mt-2 h-1.5 w-full overflow-hidden rounded-full bg-gray-200">
+							<div
+								class="h-full rounded-full bg-blue-500 transition-all duration-300"
+								style="width: {item.progress}%"
+							></div>
+						</div>
+						<p class="mt-1 text-right text-xs text-gray-400">{item.progress}%</p>
+					{/if}
+
+					{#if item.error}
+						<p class="mt-1 text-xs text-red-500">{item.error}</p>
+					{/if}
+				</li>
+			{/each}
+		</ul>
+	</div>
+{/if}