Submit Llm Task Async

Submit an LLM request for async processing. Returns a task_id immediately. Poll /research/llm/status/{task_id} for results.

This is a drop-in addition to the existing synchronous POST /research/llm endpoint. The synchronous endpoint stays COMPLETELY UNCHANGED.

Cost: 5 credits per successful response (same as sync endpoint) Note: Credits are ONLY deducted on successful LLM response. If the LLM fails, no credits are charged.

Usage from client:

1. POST /research/llm/async { prompt, temperature, max_tokens } -> { success: true, task_id: "abc123" }
2. Poll GET /research/llm/status/abc123 every 3-5 seconds -> { status: "processing" } (keep polling) -> { status: "completed", data: { response: "...", ... } } (done) -> { status: "failed", error: "..." } (error)

Tasks auto-expire after 30 minutes.