feat(agents): inject environment context into OmO system prompt

Add user time and system context to OmO agent prompt to help the model
understand the temporal context of the conversation.

Injected context includes:
- Working directory
- Platform (darwin/linux/win32)
- Current date and time
- Timezone
- Locale

Closes #51

🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/index.ts

@@ -278,6 +278,7 @@ const OhMyOpenCodePlugin: Plugin = async (ctx) => {
       const builtinAgents = createBuiltinAgents(
         pluginConfig.disabled_agents,
         pluginConfig.agents,
+        ctx.directory,
       );
 
       const userAgents = (pluginConfig.claude_code?.agents ?? true) ? loadUserAgents() : {};