## Summary

Community integration request: add an **AgentCOGS** callback (same pattern as Lago / OpenMeter) so LiteLLM proxy users can send per-completion cost to AgentCOGS for **per-customer margin** (LLM cost + revenue), aimed at B2B SaaS.

## Proposed changes

- `litellm/integrations/agentcogs.py` — `AgentCOGSLogger` → `POST /v1/ingest` - Registry entry: `callbacks: ["agentcogs"]` - Docs page: observability quickstart (env vars, `user=` attribution) - Unit tests under `tests/test_litellm/integrations/`

## PR

Incoming from: https://github.com/vaibhav11123/litellm/tree/feat/agentcogs-integration

## AgentCOGS links

- Quickstart: https://github.com/vaibhav11123/agentcogs/blob/main/docs/quickstart.md - User-landed callback (works without upstream merge): https://github.com/vaibhav11123/agentcogs/blob/main/docs/integrations/litellm.md

## Attribution

Pass `user=` on completions (same as Lago) → AgentCOGS `customer_id`.