fix(deps): downgrade zod to v3 for opencode compatibility (#3151)

opencode 1.3.16 bundles zod v3 internally and accesses _zod.def in
toJsonSchema. When oh-my-openagent installed zod v4, schemas from our
plugin caused a TypeError crash on any tool execution.

We only use basic z.* APIs with no v4-specific features, so pinning
to ^3.24.0 is safe and restores full compatibility.

package.json

@@ -69,7 +69,8 @@
     "picocolors": "^1.1.1",
     "picomatch": "^4.0.2",
     "vscode-jsonrpc": "^8.2.0",
-    "zod": "^4.1.8"
+    "zod-to-json-schema": "^3.25.1",
+    "zod": "^3.24.0"
   },
   "devDependencies": {
     "@types/js-yaml": "^4.0.9",