feat(ui): avatar crop modal, health endpoint, leaner Dockerfile

- Add AvatarCropModal.svelte using cropperjs v1: 1:1 crop, 400×400 output,
  JPEG/WebP output, dark glassmorphic UI
- Rewrite profile page avatar upload to use presigned PUT flow (POST→PUT→PATCH)
  instead of sending raw FormData directly; crop modal opens on file select
- Add GET /health → {status:ok} for Docker healthcheck
- Simplify Dockerfile: drop runtime npm ci (adapter-node bundles all deps)
- Fix docker-compose UI healthcheck: /health route, 127.0.0.1 to avoid
  IPv6 localhost resolution failure in alpine busybox wget

ui/src/lib/components/AvatarCropModal.svelte

@@ -0,0 +1,91 @@
+<script lang="ts">
+	import { onMount, onDestroy } from 'svelte';
+	import Cropper from 'cropperjs';
+	import 'cropperjs/dist/cropper.css';
+
+	interface Props {
+		file: File;
+		onconfirm: (blob: Blob, mimeType: string) => void;
+		oncancel: () => void;
+	}
+
+	let { file, onconfirm, oncancel }: Props = $props();
+
+	let imgEl: HTMLImageElement;
+	let cropper: Cropper | null = null;
+	const objectUrl = URL.createObjectURL(file);
+
+	onMount(() => {
+		cropper = new Cropper(imgEl, {
+			aspectRatio: 1,
+			viewMode: 1,
+			dragMode: 'move',
+			autoCropArea: 0.8,
+			restore: false,
+			guides: false,
+			center: true,
+			highlight: false,
+			cropBoxMovable: true,
+			cropBoxResizable: true,
+			toggleDragModeOnDblclick: false,
+			background: false
+		});
+	});
+
+	onDestroy(() => {
+		cropper?.destroy();
+		URL.revokeObjectURL(objectUrl);
+	});
+
+	function confirm() {
+		if (!cropper) return;
+		const canvas = cropper.getCroppedCanvas({ width: 400, height: 400 });
+		const mimeType = file.type === 'image/webp' ? 'image/webp' : 'image/jpeg';
+		canvas.toBlob(
+			(blob: Blob | null) => {
+				if (blob) onconfirm(blob, mimeType);
+			},
+			mimeType,
+			0.9
+		);
+	}
+</script>
+
+<!-- Backdrop -->
+<div
+	class="fixed inset-0 z-50 flex items-center justify-center bg-black/70 backdrop-blur-sm p-4"
+	role="dialog"
+	aria-modal="true"
+	aria-label="Crop profile picture"
+>
+	<div class="bg-zinc-900 rounded-2xl border border-zinc-700 shadow-2xl w-full max-w-sm flex flex-col gap-4 p-5">
+		<h2 class="text-base font-semibold text-zinc-100">Crop profile picture</h2>
+
+		<!-- Cropper image container -->
+		<div class="rounded-xl overflow-hidden bg-zinc-800" style="max-height: 340px;">
+			<img
+				bind:this={imgEl}
+				src={objectUrl}
+				alt="Crop preview"
+				style="display:block; max-width:100%;"
+			/>
+		</div>
+
+		<p class="text-xs text-zinc-500 text-center">Drag to reposition · pinch or scroll to zoom · drag corners to resize</p>
+
+		<div class="flex gap-3">
+			<button
+				onclick={oncancel}
+				class="flex-1 py-2 rounded-lg border border-zinc-600 text-zinc-300 text-sm font-medium hover:bg-zinc-700 transition-colors"
+			>
+				Cancel
+			</button>
+			<button
+				onclick={confirm}
+				class="flex-1 py-2 rounded-lg bg-amber-400 text-zinc-900 text-sm font-semibold hover:bg-amber-300 transition-colors"
+			>
+				Use photo
+			</button>
+		</div>
+	</div>
+</div>