docs: add missing zod install step to typescript-sdk and agent-migration skills

skills/openrouter-agent-migration/SKILL.md

@@ -30,6 +30,12 @@ Migrate if your code imports any of these from `@openrouter/sdk`:
 npm install @openrouter/agent
 ```
 
+The `tool()` examples below define schemas with [zod](https://zod.dev). If your project doesn't already depend on it, install it too:
+
+```bash
+npm install zod
+```
+
 If you only use agent features, you can remove `@openrouter/sdk`:
 
 ```bash

skills/openrouter-typescript-sdk/SKILL.md

@@ -22,6 +22,9 @@ npm install @openrouter/agent
 
 # For platform features (models, credits, OAuth, API keys)
 npm install @openrouter/sdk
+
+# For defining tool schemas (used by the tool() examples below)
+npm install zod
 ```
 
 ## Setup