### Description
Adds documentation for AI Governance Cost Control, including how
administrators configure budgets, how effective groups are resolved, how
enforcement works, and where spend reporting is available.
### Changes
- Replace the placeholder cost control page with a full admin guide
- Document deployment settings, group budgets, user overrides, and
effective group resolution
- Explain estimated spend, unpriced models, notifications, enforcement,
and spend reporting
- Add migration guidance for Coder Agents Cost Control
- Add screenshots for group budgets and user overrides
Closes
[AIGOV-476](https://linear.app/codercom/issue/AIGOV-476/add-documentation-for-ai-bridge-cost-controls).
> [!NOTE]
> Initially generated by Coder Agents, modified and reviewed by
@ssncferreira
Susana Ferreira
3f1973f45c
