chore: bump @opencode-ai/sdk to 1.18.21

package.json

@@ -115,7 +115,7 @@
     "@heroui/theme": "^2.4.23",
     "@lezer/highlight": "^1.2.3",
     "@octokit/rest": "^22.0.1",
-    "@opencode-ai/sdk": "1.18.18",
+    "@opencode-ai/sdk": "1.18.21",
     "@radix-ui/react-collapsible": "^1.1.12",
     "@radix-ui/react-dialog": "^1.1.15",
     "@radix-ui/react-dropdown-menu": "^2.1.16",