fix(web): make Add Section work on insecure (plain-HTTP) origins

Both add-section paths on Settings > Home Screen called crypto.randomUUID()
unguarded. Browsers only expose randomUUID in secure contexts, so on
self-hosted servers accessed over plain HTTP the click handler threw
synchronously and the Add section button appeared dead while Cancel still
worked. api/client.ts and plexAuth.ts already carried ad-hoc fallbacks for
the same problem; extract a shared lib/uuid helper (UUIDv4 via
crypto.getRandomValues, available in insecure contexts) and use it at all
four call sites.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

web/src/components/sections/SectionEditorDrawer.tsx

@@ -38,6 +38,7 @@ import {
   useAllUserCollections,
   type CollectionOption,
 } from "@/hooks/queries/useAllUserCollections";
+import { randomUUID } from "@/lib/uuid";
 
 const CATEGORY_LABELS: Record<Category, string> = {
   library_staples: "Library",
@@ -142,7 +143,7 @@ export function buildProfileSectionSaveEntry({
   }
 
   return {
-    id: section?.id ?? crypto.randomUUID(),
+    id: section?.id ?? randomUUID(),
     section_type: sectionType,
     title: title || sectionTypeLabel(sectionType),
     featured,