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/routes/upload/+page.svelte

@@ -0,0 +1,79 @@
+<script lang="ts">
+	import { goto } from '$app/navigation';
+	import { getToken } from '$lib/auth';
+	import { addToQueue, loadQueue } from '$lib/upload-queue';
+	import UploadQueue from '$lib/components/UploadQueue.svelte';
+	import { onMount } from 'svelte';
+
+	let caption = $state('');
+	let hashtags = $state('');
+	let fileInput: HTMLInputElement;
+
+	onMount(() => {
+		if (!getToken()) {
+			goto('/join');
+			return;
+		}
+		loadQueue();
+	});
+
+	async function handleFiles() {
+		const files = fileInput?.files;
+		if (!files || files.length === 0) return;
+
+		for (const file of files) {
+			await addToQueue(file, caption, hashtags);
+		}
+
+		// Reset form
+		caption = '';
+		hashtags = '';
+		if (fileInput) fileInput.value = '';
+	}
+</script>
+
+<div class="min-h-screen bg-gray-50 p-4">
+	<div class="mx-auto max-w-lg">
+		<div class="mb-6 flex items-center justify-between">
+			<h1 class="text-xl font-bold text-gray-900">Hochladen</h1>
+			<a href="/feed" class="text-sm text-blue-600 hover:underline">Zur Galerie</a>
+		</div>
+
+		<div class="rounded-lg border border-gray-200 bg-white p-4">
+			<label
+				class="flex cursor-pointer flex-col items-center justify-center rounded-lg border-2 border-dashed border-gray-300 bg-gray-50 p-8 transition hover:border-blue-400 hover:bg-blue-50"
+			>
+				<svg class="mb-2 h-10 w-10 text-gray-400" fill="none" viewBox="0 0 24 24" stroke="currentColor">
+					<path stroke-linecap="round" stroke-linejoin="round" stroke-width="1.5" d="M12 16V4m0 0l-4 4m4-4l4 4M4 20h16" />
+				</svg>
+				<span class="text-sm font-medium text-gray-600">Fotos oder Videos auswählen</span>
+				<span class="mt-1 text-xs text-gray-400">Mehrere Dateien möglich</span>
+				<input
+					bind:this={fileInput}
+					type="file"
+					accept="image/*,video/*"
+					multiple
+					class="hidden"
+					onchange={handleFiles}
+				/>
+			</label>
+
+			<div class="mt-4 space-y-3">
+				<input
+					type="text"
+					bind:value={caption}
+					placeholder="Beschreibung (optional, #hashtags möglich)"
+					class="w-full rounded-lg border border-gray-300 px-3 py-2 text-sm focus:border-blue-500 focus:outline-none focus:ring-1 focus:ring-blue-200"
+				/>
+				<input
+					type="text"
+					bind:value={hashtags}
+					placeholder="Hashtags (kommagetrennt, z.B. hochzeit, party)"
+					class="w-full rounded-lg border border-gray-300 px-3 py-2 text-sm focus:border-blue-500 focus:outline-none focus:ring-1 focus:ring-blue-200"
+				/>
+			</div>
+		</div>
+
+		<UploadQueue />
+	</div>
+</div>