Update AI Governance settings page to use new addon licensing

Context

PR https://github.com/coder/coder/pull/21598 added a new AI Governance settings page at /deployment/ai-governance that displays AI Bridge configuration options.

Once https://github.com/coder/coder/pull/21499 lands (which introduces the AI Governance addon licensing model), we should update the AI Governance page to properly integrate with the new licensing.

Tasks

• Update the AI Governance page to check for the AI Governance addon entitlement instead of just aibridge.enabled
• Consider showing different UI states based on:
  • No AI Governance addon → Show Paywall/upsell
  • AI Governance addon but AI Bridge not enabled → Show config options with guidance to enable
  • AI Governance addon with AI Bridge enabled → Show full config options
• Potentially include Boundary-related settings in the AI Governance page (since AI Governance addon includes both Bridge and Boundary features per #21499)
• Update sidebar visibility logic if needed based on addon presence

Related

• PR #21598 - feat(site): move AI Bridge settings to AI Governance page
• PR #21499 - feat: extend premium license for aigovernance
• Issue #1246 - Update licenses page to mention new verbiage around AI Governance SKU

Created on behalf of @dannykopping