feat:video player, like button, and media fallbacks

Add VideoPlayer and LikeButton components with optimistic UI and /server
endpoints for likes. Update media processor to emit WebP and JPEG
fallbacks, store fallback URLs in the DB (migration + snapshot), add
video placeholder asset, and relax CSP media-src for R2.

src/lib/components/LikeButton.svelte

@@ -0,0 +1,95 @@
+<script lang="ts">
+	import { Button } from '$lib/components/button';
+	import { Heart } from '@lucide/svelte';
+	import { toast } from 'svelte-sonner';
+
+	interface Props {
+		findId: string;
+		isLiked?: boolean;
+		likeCount?: number;
+		size?: 'sm' | 'default' | 'lg';
+		class?: string;
+	}
+
+	let {
+		findId,
+		isLiked = false,
+		likeCount = 0,
+		size = 'default',
+		class: className = ''
+	}: Props = $props();
+
+	let isLoading = $state(false);
+	let currentIsLiked = $state(isLiked);
+	let currentLikeCount = $state(likeCount);
+
+	async function toggleLike() {
+		if (isLoading) return;
+
+		const previousLiked = currentIsLiked;
+		const previousCount = currentLikeCount;
+
+		// Optimistic update
+		currentIsLiked = !currentIsLiked;
+		currentLikeCount += currentIsLiked ? 1 : -1;
+
+		isLoading = true;
+
+		try {
+			const method = currentIsLiked ? 'POST' : 'DELETE';
+			const response = await fetch(`/api/finds/${findId}/like`, {
+				method,
+				headers: {
+					'Content-Type': 'application/json'
+				}
+			});
+
+			if (!response.ok) {
+				const error = (await response.json()) as { message?: string };
+				throw new Error(error.message || 'Failed to update like');
+			}
+
+			// Success - optimistic update was correct
+		} catch (error: unknown) {
+			// Revert optimistic update on error
+			currentIsLiked = previousLiked;
+			currentLikeCount = previousCount;
+
+			console.error('Error updating like:', error);
+			toast.error('Failed to update like. Please try again.');
+		} finally {
+			isLoading = false;
+		}
+	}
+
+	// Update internal state when props change
+	$effect(() => {
+		currentIsLiked = isLiked;
+		currentLikeCount = likeCount;
+	});
+</script>
+
+<Button
+	variant="ghost"
+	{size}
+	class="group gap-1.5 {className}"
+	onclick={toggleLike}
+	disabled={isLoading}
+>
+	<Heart
+		class="h-4 w-4 transition-all duration-200 {currentIsLiked
+			? 'scale-110 fill-red-500 text-red-500'
+			: 'text-gray-500 group-hover:scale-105 group-hover:text-red-400'} {isLoading
+			? 'animate-pulse'
+			: ''}"
+	/>
+	{#if currentLikeCount > 0}
+		<span
+			class="text-sm font-medium transition-colors {currentIsLiked
+				? 'text-red-500'
+				: 'text-gray-500 group-hover:text-red-400'}"
+		>
+			{currentLikeCount}
+		</span>
+	{/if}
+</Button>