feat(web): add SwipeAction touch gesture component

Implements right-swipe-to-complete with angle-based lock-in (horizontal
must exceed 2x vertical), 100px threshold, green checkmark background
reveal, and CSS transition for snap-back and completion animation.

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

opal-web/src/lib/components/SwipeAction.svelte

@@ -0,0 +1,148 @@
+<script>
+	/**
+	 * @type {() => void}
+	 */
+	export let onSwipe;
+
+	let offsetX = 0;
+	let swiping = false;
+	let locked = false;
+	let completed = false;
+
+	/** @type {number|null} */
+	let startX = null;
+	/** @type {number|null} */
+	let startY = null;
+
+	const THRESHOLD = 100;
+
+	/**
+	 * @param {TouchEvent} e
+	 */
+	function handleTouchStart(e) {
+		if (completed) return;
+		const touch = e.touches[0];
+		startX = touch.clientX;
+		startY = touch.clientY;
+		locked = false;
+		swiping = false;
+	}
+
+	/**
+	 * @param {TouchEvent} e
+	 */
+	function handleTouchMove(e) {
+		if (completed || startX === null || startY === null) return;
+		const touch = e.touches[0];
+		const deltaX = touch.clientX - startX;
+		const deltaY = touch.clientY - startY;
+
+		if (!locked && !swiping) {
+			// Angle-based lock-in: horizontal must dominate
+			if (Math.abs(deltaX) > 10 && Math.abs(deltaX) > Math.abs(deltaY) * 2) {
+				swiping = true;
+				locked = true;
+			} else if (Math.abs(deltaY) > 10) {
+				// Vertical scroll — abort
+				startX = null;
+				startY = null;
+				return;
+			}
+		}
+
+		if (swiping) {
+			e.preventDefault();
+			// Only allow right swipe
+			offsetX = Math.max(0, deltaX);
+		}
+	}
+
+	function handleTouchEnd() {
+		if (completed || !swiping) {
+			resetState();
+			return;
+		}
+
+		if (offsetX >= THRESHOLD) {
+			completed = true;
+			// Animate to full width before firing callback
+			offsetX = window.innerWidth;
+			setTimeout(() => {
+				onSwipe();
+			}, 200);
+		} else {
+			offsetX = 0;
+		}
+		swiping = false;
+		startX = null;
+		startY = null;
+	}
+
+	function resetState() {
+		offsetX = 0;
+		swiping = false;
+		locked = false;
+		startX = null;
+		startY = null;
+	}
+
+	$: progress = Math.min(offsetX / THRESHOLD, 1);
+	$: transitioning = !swiping && offsetX !== 0;
+</script>
+
+<div
+	class="swipe-container"
+	on:touchstart={handleTouchStart}
+	on:touchmove={handleTouchMove}
+	on:touchend={handleTouchEnd}
+	on:touchcancel={resetState}
+>
+	<div
+		class="swipe-background"
+		style:opacity={progress}
+	>
+		<svg class="check-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor">
+			<path stroke-linecap="round" stroke-linejoin="round" stroke-width="3" d="M5 13l4 4L19 7" />
+		</svg>
+	</div>
+
+	<div
+		class="swipe-content"
+		class:transitioning
+		style:transform="translateX({offsetX}px)"
+	>
+		<slot />
+	</div>
+</div>
+
+<style>
+	.swipe-container {
+		position: relative;
+		overflow: hidden;
+		touch-action: pan-y;
+	}
+
+	.swipe-background {
+		position: absolute;
+		inset: 0;
+		background-color: var(--color-success);
+		display: flex;
+		align-items: center;
+		padding-left: var(--spacing-lg);
+	}
+
+	.check-icon {
+		width: 1.5rem;
+		height: 1.5rem;
+		color: white;
+	}
+
+	.swipe-content {
+		position: relative;
+		background-color: var(--bg-primary);
+	}
+
+	.swipe-content.transitioning {
+		transition: transform 0.2s ease-out;
+	}
+</style>