refactor(omo-task): rename to call_omo_agent with run_in_background parameter

- Rename omo-task to call-omo-agent with mandatory run_in_background parameter
- Implement background mode using BackgroundManager (fire-and-forget abort)
- Implement sync mode with existing subagent logic
- Fix background_cancel: use fire-and-forget abort to prevent parent session interruption
- Add call_omo_agent to tool disable list in explore/librarian agents
- Add call_omo_agent to tool disable list in BackgroundManager

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

src/tools/index.ts

@@ -33,7 +33,7 @@ import type { BackgroundManager } from "../features/background-agent"
 
 type OpencodeClient = PluginInput["client"]
 
-export { createOmoTask } from "./omo-task"
+export { createCallOmoAgent } from "./call-omo-agent"
 
 export function createBackgroundTools(manager: BackgroundManager, client: OpencodeClient) {
   return {