fix: include generated id in createComment POST body

The book_comments collection has a custom 'id' field (type: text,
required: true) distinct from PocketBase's system record ID.
Every comment POST was returning 400 validation_required because
the id field was never sent.

Fix: generate a 15-char hex ID via crypto.randomUUID() and include
it in the payload, matching PocketBase's own ID alphabet.

ui/src/lib/server/pocketbase.ts

@@ -1530,6 +1530,7 @@ export async function createComment(
 		method: 'POST',
 		headers: { Authorization: `Bearer ${token}`, 'Content-Type': 'application/json' },
 		body: JSON.stringify({
+			id: crypto.randomUUID().replace(/-/g, '').slice(0, 15),
 			slug,
 			chapter,
 			body,