fix: resolve SvelteKit route conflict by moving vote endpoint to /api/comment/[id]/vote

/api/comments/[id] and /api/comments/[slug] were ambiguous dynamic segments at
the same path level, causing a build error. Moved the vote handler to the
singular /api/comment/ prefix and updated all callers (web + iOS).

ui/src/lib/components/CommentsSection.svelte

@@ -180,7 +180,7 @@
 		if (votingIds.has(commentId)) return;
 		votingIds = new Set([...votingIds, commentId]);
 		try {
-			const res = await fetch(`/api/comments/${commentId}/vote`, {
+			const res = await fetch(`/api/comment/${commentId}/vote`, {
 				method: 'POST',
 				headers: { 'Content-Type': 'application/json' },
 				body: JSON.stringify({ vote: v })