Add admin template deletion with broadcast to all hosts

- DELETE /v1/admin/templates/{name} endpoint (admin-only)
- Broadcasts DeleteSnapshot RPC to all online hosts before removing DB record
- Frontend admin templates page uses deleteAdminTemplate() instead of
  team-scoped deleteSnapshot()
- Delete button shown for all template types, not just snapshots

frontend/src/lib/api/builds.ts

@@ -64,3 +64,7 @@ export type AdminTemplate = {
 export async function listAdminTemplates(): Promise<ApiResult<AdminTemplate[]>> {
 	return apiFetch('GET', '/api/v1/admin/templates');
 }
+
+export async function deleteAdminTemplate(name: string): Promise<ApiResult<void>> {
+	return apiFetch('DELETE', `/api/v1/admin/templates/${name}`);
+}