feat(03-02): create ImageUpload component with drag-drop

- Add drag-and-drop zone for image uploads
- Show optimistic preview during upload
- Support keyboard navigation (Enter/Space to trigger)
- Handle upload via fetch to ?/uploadImage action
- Clean up object URLs after upload completes
- Provide callbacks for upload lifecycle events

src/lib/components/ImageUpload.svelte

@@ -0,0 +1,164 @@
+<script lang="ts">
+	import { invalidateAll } from '$app/navigation';
+
+	interface Props {
+		entryId: string;
+		onUploadStart?: () => void;
+		onUploadComplete?: (imageId: string) => void;
+		onUploadError?: (error: string) => void;
+	}
+
+	let { entryId, onUploadStart, onUploadComplete, onUploadError }: Props = $props();
+
+	let isDragging = $state(false);
+	let isUploading = $state(false);
+	let previewUrl: string | null = $state(null);
+	let fileInput: HTMLInputElement;
+
+	function handleDragOver(e: DragEvent) {
+		e.preventDefault();
+		isDragging = true;
+	}
+
+	function handleDragLeave(e: DragEvent) {
+		e.preventDefault();
+		isDragging = false;
+	}
+
+	function handleDrop(e: DragEvent) {
+		e.preventDefault();
+		isDragging = false;
+
+		const file = e.dataTransfer?.files[0];
+		if (file && file.type.startsWith('image/')) {
+			uploadFile(file);
+		}
+	}
+
+	function handleFileSelect(e: Event) {
+		const input = e.target as HTMLInputElement;
+		const file = input.files?.[0];
+		if (file) {
+			uploadFile(file);
+		}
+	}
+
+	async function uploadFile(file: File) {
+		// Validate image type
+		if (!file.type.startsWith('image/')) {
+			onUploadError?.('File must be an image');
+			return;
+		}
+
+		// Create optimistic preview
+		previewUrl = URL.createObjectURL(file);
+		onUploadStart?.();
+		isUploading = true;
+
+		try {
+			const formData = new FormData();
+			formData.append('image', file);
+			formData.append('entryId', entryId);
+
+			const response = await fetch('?/uploadImage', {
+				method: 'POST',
+				body: formData
+			});
+
+			const result = await response.json();
+
+			if (result.type === 'failure') {
+				const errorMsg = result.data?.error || 'Upload failed';
+				onUploadError?.(errorMsg);
+			} else if (result.type === 'success') {
+				onUploadComplete?.(result.data?.imageId);
+				await invalidateAll();
+			}
+		} catch (err) {
+			console.error('Upload error:', err);
+			onUploadError?.('Network error during upload');
+		} finally {
+			// Cleanup
+			if (previewUrl) {
+				URL.revokeObjectURL(previewUrl);
+				previewUrl = null;
+			}
+			isUploading = false;
+			// Reset file input
+			if (fileInput) {
+				fileInput.value = '';
+			}
+		}
+	}
+
+	function handleKeydown(e: KeyboardEvent) {
+		if (e.key === 'Enter' || e.key === ' ') {
+			e.preventDefault();
+			fileInput?.click();
+		}
+	}
+</script>
+
+<div
+	class="relative border-2 border-dashed rounded-lg p-4 text-center transition-colors cursor-pointer min-h-[100px] flex items-center justify-center {isDragging
+		? 'border-blue-500 bg-blue-50'
+		: 'border-gray-300 hover:border-gray-400'}"
+	ondragover={handleDragOver}
+	ondragleave={handleDragLeave}
+	ondrop={handleDrop}
+	role="button"
+	tabindex="0"
+	onclick={() => fileInput?.click()}
+	onkeydown={handleKeydown}
+>
+	<input
+		bind:this={fileInput}
+		type="file"
+		accept="image/*"
+		onchange={handleFileSelect}
+		class="hidden"
+	/>
+
+	{#if isUploading}
+		<div class="flex flex-col items-center gap-2">
+			{#if previewUrl}
+				<img src={previewUrl} alt="Preview" class="w-16 h-16 object-cover rounded opacity-50" />
+			{/if}
+			<div class="flex items-center gap-2 text-gray-500">
+				<svg
+					class="w-5 h-5 animate-spin"
+					xmlns="http://www.w3.org/2000/svg"
+					fill="none"
+					viewBox="0 0 24 24"
+				>
+					<circle class="opacity-25" cx="12" cy="12" r="10" stroke="currentColor" stroke-width="4"
+					></circle>
+					<path
+						class="opacity-75"
+						fill="currentColor"
+						d="M4 12a8 8 0 018-8V0C5.373 0 0 5.373 0 12h4zm2 5.291A7.962 7.962 0 014 12H0c0 3.042 1.135 5.824 3 7.938l3-2.647z"
+					></path>
+				</svg>
+				<span class="text-sm">Uploading...</span>
+			</div>
+		</div>
+	{:else}
+		<div class="flex flex-col items-center gap-2 text-gray-500">
+			<svg
+				class="w-8 h-8"
+				xmlns="http://www.w3.org/2000/svg"
+				fill="none"
+				viewBox="0 0 24 24"
+				stroke="currentColor"
+			>
+				<path
+					stroke-linecap="round"
+					stroke-linejoin="round"
+					stroke-width="2"
+					d="M4 16l4.586-4.586a2 2 0 012.828 0L16 16m-2-2l1.586-1.586a2 2 0 012.828 0L20 14m-6-6h.01M6 20h12a2 2 0 002-2V6a2 2 0 00-2-2H6a2 2 0 00-2 2v12a2 2 0 002 2z"
+				/>
+			</svg>
+			<span class="text-sm">Drop image or click to upload</span>
+		</div>
+	{/if}
+</div>