docs: remove AI Governance Add-On references (#28073)

## Summary

Replaces all remaining "AI Governance Add-On" references with language
consistent with AI Governance being included with a Premium license.

**`docs/ai-coder/ai-gateway/standalone.md`**

- Admonition: "AI Gateway requires the AI Governance Add-On...
deployments without the add-on will not be able to access" → "AI Gateway
requires a Premium license. Community deployments cannot access AI
Gateway."
- Requirements list: "A Coder license with the AI Governance Add-On" →
"A Premium license with AI Governance"

**`docs/install/airgap.md`**

- Table row: "deployments with the AI Governance Add On" → "deployments
with AI Governance"

**`docs/reference/glossary.md`**

- Agent Firewall, AI Gateway, AI Gateway Proxy entries: "This feature
requires the AI Governance Add-On" → "This feature requires a Premium
license"
- Agent Workspace Build entry: "the AI Governance Add-On expands the
allowance" → "a Premium license expands the allowance"
- Heading: "### AI Governance Add-On" → "### AI Governance"
- Definition: "A separate per-user license for Premium customers,
purchased on top of a Premium subscription..." → "Included with a
Premium license, AI Governance unlocks..."

**`docs/ai-coder/ai-governance.md`**

- Removed the "Identifying AI seat consumers" section (heading through
end of file), which described an "AI add-on column" in the UI

## Note

References to Agent Workspace Builds will be eliminated in a separate PR
that removes Coder Tasks from the docs.

---

PR generated with Coder Agents.

docs/ai-coder/ai-gateway/standalone.md

@@ -1,9 +1,8 @@
 # Deploy AI Gateway as a standalone service
 
 > [!NOTE]
-> AI Gateway requires the [AI Governance Add-On](../ai-governance.md).
-> As of Coder v2.32, deployments without the add-on will not be able to
-> access AI Gateway.
+> AI Gateway requires a [Premium](../ai-governance.md) license.
+> Community deployments cannot access AI Gateway.
 
 When AI traffic needs dedicated compute, independent scaling, or a separate network endpoint, you can deploy AI Gateway separately from the Coder control plane (`coderd`).
 
@@ -15,7 +14,7 @@ A standalone AI Gateway serves client traffic on its own listener and maintains
 Standalone AI Gateway requires:
 
 - Coder v2.36.0 or later.
-- A Coder license with the [AI Governance Add-On](../ai-governance.md).
+- A [Premium license with AI Governance](../ai-governance.md).
 - AI Gateway enabled on the Coder control plane with `CODER_AI_GATEWAY_ENABLED=true` or `--ai-gateway-enabled=true`.
 - The full Coder image or a Coder binary that includes the `coder ai-gateway start` command.
 

docs/ai-coder/ai-governance.md

@@ -143,17 +143,3 @@ entitlement limits.
 
 <small>Agent Workspace Build usage showing current consumption against
 entitlement limits in the Licenses page.</small>
-
-## Identifying AI seat consumers
-
-When AI Governance is licensed, the **Users** table and
-**Organization Members** table display an **AI add-on** column that shows
-whether each user is consuming an AI seat:
-
-- A green check icon indicates the user is actively consuming an AI seat.
-- A gray X icon indicates the user is not consuming an AI seat.
-
-A user consumes an AI seat when they use AI features such as AI Gateway or
-Tasks. The column helps administrators identify which users contribute to
-the organization's AI seat count, making it easier to manage seat
-allocations and stay within license limits.