feat(omo-task): add agent orchestration tool for subagent spawning

Implement omo_task tool that allows main agents (oracle, frontend-ui-ux-engineer, etc.) to spawn explore or librarian as subagents.

- Add constants: ALLOWED_AGENTS, TASK_TOOL_DESCRIPTION_TEMPLATE
- Add types: AllowedAgentType, OmoTaskArgs, OmoTaskResult
- Implement createOmoTask function with session management
- Support both new session creation and existing session continuation
- Include proper error handling and logging

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src/tools/omo-task/constants.ts

@@ -0,0 +1,17 @@
+export const ALLOWED_AGENTS = ["explore", "librarian"] as const
+
+export const TASK_TOOL_DESCRIPTION_TEMPLATE = `Launch a new agent to handle complex, multi-step tasks autonomously.
+
+This is a restricted version of the Task tool that only allows spawning explore and librarian agents.
+
+Available agent types:
+{agents}
+
+When using this tool, you must specify a subagent_type parameter to select which agent type to use.
+
+Usage notes:
+1. Launch multiple agents concurrently whenever possible, to maximize performance
+2. When the agent is done, it will return a single message back to you
+3. Each agent invocation is stateless unless you provide a session_id
+4. Your prompt should contain a highly detailed task description for the agent to perform autonomously
+5. Clearly tell the agent whether you expect it to write code or just to do research`