Measure & Report AI Governance Seat Usage

> [!NOTE]
> This issue is a part of our larger **AI Governance Add-On**: [PRD](https://www.notion.so/coderhq/AI-Governance-Add-On-2ced579be592801eac50c83982a0fa49). See the [GitHub Project](https://github.com/orgs/coder/projects/84/views/2) for all related issues.

Our AI Governance Add-On (released in February) includes a number of seats, which can be a subset of the number of users within a Coder deployment. In the March release, we want to begin measuring and reporting to admins (and to tallyman) the number of seats consumed using AI Governance features (Bridge, Boundaries, Tasks).

### Measurement

- **AI Governance Seats**: Similar to our agent-ready workspace starts measurement, our collector and Tallyman should measure AI Governance seats as users who have done 1 of the following activities:
- Authenticated to AI Bridge and sent at least 1 request
- Created an AI Task
- Leveraged a workspace with Boundaries (not in scope to be measured yet)

### Collection & Display

- [ ] This should be displayed in the licensing page under Agent-Ready Workspace starts as "AI Governance Users."
- [ ] This should also be sent as a tallyman metric

### Enforcement & Warnings

- [ ] **Warning banner:** When an overage occurs (# of users > # entitled AI governance seats), a warning should show only to admins and an overage should be reported via Metronome/Tallyman.

### Out of scope

- **Fine-grained controls**: Controls for admins to specify which users/seats can see/use AI governance features is out of scope for this specific issue.