fix: allow visibility-only setup updates without name

updateSetupSchema required name as mandatory, causing ZodError when
ShareModal sent visibility-only updates. Made name optional in update
schema and guarded against setting undefined name in service layer.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/shared/schemas.ts

@@ -96,7 +96,7 @@ export const createSetupSchema = z.object({
 });
 
 export const updateSetupSchema = z.object({
-	name: z.string().min(1, "Setup name is required"),
+	name: z.string().min(1, "Setup name is required").optional(),
 	visibility: z.enum(["private", "link", "public"]).optional(),
 });